In the world of cybersecurity, particularly in hardware security research and embedded system defense, glitching attacks have emerged as powerful tools for attackers and researchers alike. These techniques fall under the broader umbrella of fault injection, which refers to deliberately introducing errors into a system in order to bypass protections or extract sensitive information. Glitching attacks are especially dangerous because they do not require permanent changes to hardware. Instead, they rely on creating very short and precise disruptions in the system’s electrical behavior, such as fluctuations in power, manipulations of the clock signal, or interference with the reset line. These small faults can force a system into unexpected states, skipping over security checks or crashing into unprotected modes.
Understanding glitching is crucial for cybersecurity professionals, ethical hackers, and embedded system developers. As devices become more interconnected and security-critical—especially in sectors like automotive, finance, healthcare, and defense—the importance of hardware-level protections continues to grow. Fault injection techniques such as glitching offer a unique lens through which to assess and fortify the security of embedded systems. Unlike traditional software attacks, glitching operates on a physical layer, which means it can bypass protections that software developers may consider secure or even invulnerable.
This first part of our deep dive into glitching will introduce the concept of fault injection in cybersecurity, define glitching and its significance, and explore why it is such an effective method for compromising devices. The later parts will explore the specific techniques of power glitching, clock glitching, and reset glitching, along with tools, case studies, and strategies for defense.
Understanding Fault Injection in Hardware Security
Fault injection is a category of attack in which an adversary deliberately induces errors into a device to alter its normal operation. These faults can be created through various physical means including voltage fluctuations, laser beams, electromagnetic pulses, and clock signal manipulations. The main goal of fault injection is to exploit vulnerabilities in timing or execution logic that cannot be accessed through traditional software-based attacks.
The value of fault injection lies in its ability to break systems without breaking them physically. This means the same device can be tested or attacked repeatedly without any visible signs of tampering. In practical terms, an attacker can attempt hundreds or thousands of fault injections in order to find just the right moment to glitch the system. When timed correctly, the glitch can cause the device to skip important security checks, leak sensitive data like encryption keys, or enter a debug or maintenance mode that is normally inaccessible.
Fault injection is not just a tool for attackers. It is also a valuable method for testing system robustness during development. Security researchers and hardware developers use these techniques to identify weaknesses in microcontrollers, firmware, and bootloaders. By anticipating how a device might behave under unusual physical conditions, engineers can build more secure systems that are resistant to real-world attacks.
What Is Glitching in Cybersecurity
Glitching refers specifically to a type of fault injection where brief, high-precision disruptions are introduced into key signals of a system, such as its power supply, clock signal, or reset line. These disruptions, known as glitches, are designed to be short enough not to damage the device but precise enough to cause the system to behave unpredictably. When done correctly, glitching can bypass authentication routines, alter execution paths, or trigger failure modes that benefit the attacker.
Glitching is especially relevant in the context of embedded systems, which often rely on tightly controlled timing mechanisms. These systems include devices like routers, smartcards, digital locks, IoT devices, and automotive controllers. The security of such systems depends heavily on predictable signal behavior. A sudden voltage drop, a corrupted clock pulse, or an improperly timed reset can all cause the system to behave in unintended ways.
In a successful glitching attack, the device is typically forced into a state that was never intended by its designers. This might mean skipping over a check for a valid password, misinterpreting a signature verification, or executing unintended code. Because glitching exploits physical properties of the hardware, it often succeeds where software-based attacks fail. It is not uncommon for a device that is fully patched and secure against traditional attacks to still be vulnerable to glitching.
Glitching does not require invasive tools like microprobing or decapsulation. Instead, attackers use external equipment to generate glitches through contact points like test pins, power lines, or external interfaces. This makes glitching relatively accessible for well-equipped security researchers or attackers with modest resources. Additionally, glitching can be highly targeted. Attackers can time their glitches to coincide with specific operations, such as when the system is verifying a password or loading secure firmware, increasing the chances of success.
Why Glitching Is a Powerful Attack Vector
Glitching attacks are considered powerful for several reasons. First, they exploit the physical nature of digital systems, which are often assumed to be reliable and deterministic. In reality, electronic systems are vulnerable to very small, carefully crafted disruptions. This discrepancy between theoretical security and physical vulnerability is what makes glitching so effective.
Second, glitching does not leave a trace in the software logs or memory. Because it affects only the physical execution of instructions, it can be nearly invisible to traditional security monitoring. This stealth makes it ideal for attackers who want to remain undetected while attempting to bypass protections.
Third, glitching is non-destructive. Unlike invasive hardware attacks that require opening the chip package or tampering with internal circuits, glitching can be performed externally. Devices that are successfully attacked using glitching techniques remain functional, allowing the attacker to continue using them, extract more data, or repeat the attack as needed.
Another key advantage is the precision that glitching allows. Modern tools enable attackers to time their glitches down to a single clock cycle. This high degree of control means that glitches can be delivered exactly when the target operation is being executed, such as during a secure boot process or while checking a password. With sufficient trial and error, attackers can find the exact conditions needed to achieve a successful bypass.
Furthermore, glitching is effective across a wide range of devices and industries. It has been used to compromise everything from gaming consoles and payment terminals to military-grade secure elements. The ubiquity of embedded systems in modern technology means that any device with inadequate physical security could potentially be vulnerable to glitching attacks.
Finally, glitching offers a high return on investment for attackers. With the right knowledge and equipment, a successful glitch can yield access to encrypted data, proprietary firmware, or secure authentication mechanisms. For researchers, this means uncovering valuable security flaws that can be reported and fixed. For malicious actors, it can mean stealing credentials, cloning devices, or launching further attacks.
The Role of Timing and Voltage in Glitching
At the heart of glitching is the manipulation of two key parameters: timing and voltage. These elements determine how digital systems operate and respond to inputs. Timing refers to the sequence and duration of electrical signals that control how instructions are executed. Voltage refers to the power levels supplied to various components of the system. By altering either one at just the right moment, attackers can interfere with normal operation.
Most embedded systems are designed to operate within strict timing margins. For example, a password check might be scheduled to occur exactly 100 microseconds after a reset. If the attacker can inject a glitch just before or during that check, they may cause the check to be skipped or corrupted. This timing precision is what makes glitching a skillful and technical attack method.
Voltage manipulation works on a similar principle. Digital logic circuits rely on specific voltage thresholds to interpret binary values. If the voltage is dropped or surged at the right moment, the circuit might misinterpret a ‘0’ as a ‘1’ or vice versa. This can corrupt instructions, change control flow, or cause the system to behave erratically. However, if the glitch is too long or too powerful, it may crash or damage the system. Therefore, effective glitching requires a balance between strength and precision.
To deliver glitches with the necessary accuracy, attackers use specialized equipment such as signal generators, voltage modulators, and timing analyzers. Tools like ChipWhisperer or custom glitcher boards allow for fine-grained control over glitch parameters. These tools can synchronize with the target device’s operations using side-channel signals like electromagnetic emissions or power consumption. Once synchronized, the glitching tool can inject faults at precisely the right moment, maximizing the chances of success.
Glitching techniques are most effective when the attacker has detailed knowledge of the device’s behavior. This knowledge can come from reverse engineering, documentation, or trial and error. By analyzing how the system behaves under normal conditions, the attacker can predict where and when to apply the glitch. For instance, if a certain memory region is accessed during authentication, the attacker might target that specific moment to cause a fault.
Glitching is not a guaranteed method. It often involves repeated testing and fine-tuning. But when it works, the results can be devastating. A single well-timed glitch can render secure boot protections ineffective or allow unauthorized firmware to execute. This level of impact makes glitching a top concern for hardware security experts and a valuable technique for those looking to explore the boundaries of embedded system vulnerabilities.
Understanding Power Glitching in Hardware Attacks
Power glitching is one of the most foundational and widely used fault injection techniques in the field of hardware security. It involves introducing brief, controlled interruptions or modifications to the power supply of a target device. These short disturbances are designed to be subtle enough to avoid crashing the system outright, yet forceful enough to alter the execution of critical instructions. The goal is to cause the system to behave in unintended ways, often skipping security checks or executing corrupted code paths.
In embedded systems, every digital operation relies on a steady and predictable power supply. When power fluctuates outside the expected range, logic gates within the microcontroller or processor may fail to function correctly. A voltage drop at just the right moment can result in corrupted memory fetches, malformed instruction decoding, or skipped verifications. Because the system’s hardware remains intact and operational, this method allows attackers to experiment repeatedly, fine-tuning the timing and strength of each glitch until the desired effect is achieved.
Power glitching is favored among attackers because of its relative simplicity and effectiveness. With the right tools and timing knowledge, an attacker can induce power faults externally, often through accessible pins or exposed circuitry. This method does not require disassembling or altering the device physically, making it a practical approach in both research and real-world exploitation scenarios.
How Power Glitching Alters System Behavior
To understand how power glitching works at a technical level, it is essential to look at how embedded processors handle instruction execution. A typical microcontroller fetches instructions from memory and processes them based on a predefined timing cycle. These operations are governed by the processor’s internal clock and powered by a consistent voltage supply. When the voltage drops too low, the transistors within the chip may operate more slowly, fail to switch states properly, or behave unpredictably.
In this unstable state, the processor may misinterpret an instruction, skip it entirely, or generate a fault that causes the system to enter a different execution path. For instance, during a password comparison routine, if the glitch occurs just as the device reads or compares data, it might erroneously register the check as successful. Similarly, during secure boot processes, a brief drop in voltage might cause the device to skip signature validation routines or misload protected firmware.
The key to successful power glitching lies in controlling the timing of the glitch down to microsecond or even nanosecond precision. Triggering the glitch too early or too late might have no effect or could cause the system to reset or crash. However, a well-timed glitch can exploit small timing windows in critical functions, leading to highly effective bypasses of security mechanisms.
Attackers often use side-channel information to determine when to deliver the glitch. Side-channel signals, such as power consumption traces or electromagnetic emissions, can reveal when specific operations are taking place. By aligning the glitch injection with these signals, attackers can increase the likelihood of a successful attack without knowing the exact inner workings of the device.
Real-World Applications of Power Glitching
Power glitching has been successfully applied in a range of real-world attacks across industries. In consumer electronics, one notable example is the exploitation of gaming consoles. In the case of a popular console from the early 2010s, security researchers used power glitching to bypass the signature verification during the boot process. This allowed them to execute unauthorized code, install custom firmware, and effectively jailbreak the system. This attack demonstrated how a single, well-timed glitch could break a previously secure chain of trust.
In the financial sector, power glitching has been used to attack smartcards and secure elements used in payment systems. These devices often perform cryptographic operations and key comparisons in hardware. By glitching the power during these operations, attackers have managed to bypass authentication routines or extract partial cryptographic keys. Even though these devices are designed with tamper resistance in mind, power glitching continues to be an effective method of compromising them under the right conditions.
Automotive systems have also proven vulnerable to power glitching. Electronic Control Units (ECUs) used in modern vehicles often rely on secure boot mechanisms to prevent unauthorized firmware from being loaded. Researchers have demonstrated that power glitching can be used to bypass these boot protections, potentially allowing attackers to inject malicious code or disable critical safety features. Given the increasing reliance on software-defined vehicles, such vulnerabilities have serious implications for vehicle safety and privacy.
In industrial and IoT applications, power glitching has enabled attackers to bypass login mechanisms, unlock administrative interfaces, or extract firmware from otherwise protected devices. As these systems are often deployed in remote or unsecured environments, the risk of physical access by attackers increases, making power glitching a particularly attractive attack method.
Tools and Techniques for Executing Power Glitching
Executing a successful power glitch attack requires a combination of precise timing control and specialized hardware. The basic setup involves a power supply capable of delivering controlled voltage variations, a trigger mechanism to determine when to inject the glitch, and monitoring tools to observe the effects of the attack.
One of the most commonly used platforms for power glitching is a fault injection toolkit that integrates a programmable glitch module with timing controls and signal monitoring. These platforms allow researchers to configure parameters such as glitch delay, duration, amplitude, and trigger source. By iterating through combinations of these settings, attackers can find the optimal glitch configuration for a given target.
The trigger mechanism is often based on side-channel signals or observable system behavior. For example, attackers might monitor the target device’s serial output, LED activity, or power trace to determine when a critical operation is taking place. Once the trigger condition is detected, the glitch module injects a short dip in the power supply, aiming to corrupt the ongoing operation.
For more advanced setups, oscilloscopes and logic analyzers are used to capture precise signal behavior before and after the glitch. This data helps fine-tune the glitch parameters and confirms whether the fault had the intended effect. In some cases, attackers use custom firmware on the target device to create observable markers, such as known outputs or debug messages, which help determine the success of the glitch.
In practice, a successful power glitching attack may require thousands of trials. Each attempt slightly adjusts the glitch parameters and monitors for behavioral changes. Over time, this iterative process reveals which glitch configurations are most effective at compromising the device. Once an effective configuration is found, the attacker can repeat it consistently to bypass security protections at will.
Vulnerabilities Exploited by Power Glitching
The success of power glitching depends largely on design weaknesses in the target system. Many embedded systems assume a stable power environment and lack the mechanisms to detect or recover from brief voltage anomalies. This assumption creates opportunities for attackers to introduce glitches without triggering alerts or causing permanent damage.
One common vulnerability is the absence of voltage monitoring circuits. Secure systems should include power integrity checks that detect unusual voltage patterns and halt execution if a fault is detected. However, cost or complexity constraints often lead designers to omit these features, especially in consumer-grade devices.
Another weakness is the reliance on unprotected bootloaders or firmware routines. If these routines do not verify their integrity after a fault or if they fail open rather than fail safe, they can be bypassed using a well-timed glitch. In some cases, a simple memory corruption caused by a power glitch is enough to redirect execution to unintended code paths or expose debugging interfaces.
Lack of execution redundancy is also a contributing factor. Systems that perform security-critical checks only once, without cross-verification or integrity validation, are particularly vulnerable. A single corrupted execution due to a glitch may be sufficient to compromise the system. Implementing dual checks, hash verifications, or mirrored logic can reduce the effectiveness of power glitching by requiring multiple faults to succeed.
Additionally, exposed hardware interfaces such as test points, UART headers, or JTAG interfaces make power glitching more accessible. These interfaces often provide access to power lines or allow observation of system behavior, enabling attackers to synchronize their glitching efforts. Proper shielding and disabling of unused interfaces can help reduce the risk.
Mitigating the Threat of Power Glitching
Defending against power glitching requires a combination of hardware design best practices, fault detection mechanisms, and software-level redundancy. The first step is to ensure that the power supply circuitry includes filters and stabilizers that can resist sudden voltage changes. Capacitors, inductors, and voltage regulators can help smooth out fluctuations and reduce the effectiveness of glitch injections.
Secure microcontrollers and cryptographic modules should implement tamper detection features that monitor for anomalies in power levels, temperature, or electromagnetic emissions. When such anomalies are detected, the system should enter a secure halt state, reset, or wipe sensitive data to prevent exploitation.
At the software level, implementing redundancy in security checks can greatly reduce the impact of a successful glitch. For example, validating a password using two separate routines, checking firmware integrity in multiple stages, or performing continuous validation during execution can increase resilience. These measures ensure that a single fault does not compromise the entire system.
Bootloaders and firmware should include cryptographic signatures and integrity checks that are verified at multiple points during the boot process. If any fault is detected during verification, the system should reject the boot and enter a safe state. Developers should avoid relying on single-point-of-failure logic in secure paths.
Finally, obfuscating critical operations or randomizing execution timing can make glitching significantly harder. If the timing of security checks is not predictable, it becomes much more difficult for attackers to synchronize their glitches. While not foolproof, these techniques increase the cost and complexity of a successful attack.
Exploring Clock Glitching in Fault Injection Attacks
Clock glitching is a powerful and targeted fault injection technique that disrupts the timing signals controlling the execution of digital systems. Unlike power glitching, which alters the voltage levels of a system, clock glitching focuses on manipulating the clock signal that governs the sequencing and synchronization of operations inside a microcontroller or processor. By introducing brief, abnormal pulses or distortions into the system clock, attackers can force the device to skip, misinterpret, or incorrectly process instructions.
The clock signal acts as the heartbeat of an embedded system, determining when and how instructions are fetched, decoded, and executed. If the clock is temporarily accelerated or distorted at a critical moment, the system may process an instruction incorrectly, skip over a conditional check, or enter an unintended execution path. This behavior can be harnessed to bypass authentication, break cryptographic routines, or access restricted functions.
Clock glitching is considered more precise than power glitching because it targets the temporal control mechanism directly. With specialized tools, attackers can inject extra clock edges, shorten clock cycles, or introduce malformed waveforms, all timed to critical operations. This level of control makes clock glitching especially effective in systems that perform fast and sensitive tasks, such as secure boot procedures or encrypted communication sessions.
The Role of the System Clock in Embedded Devices
To understand how clock glitching works, it is important to examine the role of the system clock in digital electronics. In most microcontrollers and processors, the system clock determines the rhythm at which operations are executed. Each instruction is processed over one or more clock cycles, which consist of rising and falling edges that coordinate logic transitions within the chip.
During a typical instruction cycle, the processor fetches an instruction from memory, decodes it, reads or writes to memory, and then executes the instruction. These steps rely on a stable and well-defined clock. If the clock pulse is malformed—either too fast, too short, or occurring at the wrong time—the processor may fail to complete an operation or interpret the data incorrectly.
By exploiting this reliance on clock timing, attackers can insert glitches that cause the processor to misbehave without altering the system’s code or memory. For example, a brief acceleration of the clock may cause a timing-dependent comparison to be skipped. Alternatively, injecting an additional pulse during a memory access could result in data corruption or instruction skipping. These behaviors are not normally possible through software and can only be triggered through physical manipulation of the clock signal.
Most embedded systems use external crystal oscillators or internal clock generators, which can be influenced through exposed test points or power lines. This makes it possible for attackers to introduce glitches externally using synchronized hardware tools. Since the manipulation occurs at a fundamental level, many protections implemented in software are ineffective against clock glitching.
How Clock Glitching Bypasses Security
Clock glitching is particularly effective in defeating security measures that depend on strict instruction timing or conditional execution. Secure bootloaders, password check routines, and cryptographic verification processes often include steps that must be executed correctly and in sequence. By disrupting the clock at the exact moment these steps occur, attackers can cause the system to skip or mis-execute them.
For instance, consider a routine that checks whether a user-provided password matches a stored value. This comparison may occur in just a few clock cycles. If a clock glitch is injected during this window, the system might falsely register the check as successful or fail to complete the comparison at all. Similarly, secure bootloaders often validate firmware signatures before executing code. A glitch during the signature verification could result in the system proceeding to load unsigned or malicious code.
Unlike power glitching, clock glitching typically does not affect the voltage thresholds of logic gates. This makes it a more targeted approach, less likely to crash the system or cause widespread instability. It also means that clock glitching can be used on devices that include power integrity monitoring or tamper detection mechanisms that would normally detect voltage anomalies.
Another advantage of clock glitching is its precision. High-end glitching platforms allow attackers to synchronize glitch pulses with sub-microsecond accuracy. This precision enables them to align the glitch with specific instruction sequences, increasing the probability of bypassing protections without interfering with unrelated operations. Because many embedded systems perform critical checks very quickly, this level of timing control is essential for success.
Tools and Techniques for Clock Glitching
Successful clock glitching requires a combination of specialized hardware and detailed knowledge of the target system’s timing characteristics. The most common setup includes a controllable clock source, a trigger mechanism, and a monitoring system to observe the effects of each glitch attempt.
One of the most effective methods involves replacing the device’s normal clock source with a controllable signal generator. This allows the attacker to inject malformed pulses, temporarily increase or decrease the clock frequency, or add extra clock edges at precise moments. These signal generators are often programmable and capable of being synchronized with other inputs, such as serial output, electromagnetic emissions, or GPIO signals from the target device.
The glitch timing is usually guided by side-channel analysis or behavior observation. For example, an attacker might monitor the device’s UART output or LED behavior to detect when a password check is occurring. Once this event is detected, the glitch module injects a manipulated clock pulse to disrupt the process. Timing can be refined using logic analyzers or oscilloscopes to measure signal changes with high precision.
High-end tools such as fault injection frameworks often include integrated clock glitching capabilities, complete with user interfaces for setting glitch parameters and viewing results. These tools allow for automated testing of thousands of glitch configurations, helping the attacker discover effective timing windows through experimentation. Each attempt can be logged and analyzed to identify which glitches had a measurable effect on the system.
Custom clock circuits can also be used to fine-tune glitch behavior. For example, a glitch injector may generate a clean clock signal for normal operation, then switch to a distorted signal for a single cycle before returning to the standard waveform. This approach minimizes disruption to the overall system while maximizing the chances of causing a targeted fault.
Devices Vulnerable to Clock Glitching
Clock glitching can be applied to a wide range of devices, including microcontrollers, secure processors, and system-on-chips that rely on deterministic execution behavior. Devices commonly targeted include those found in consumer electronics, secure access control systems, and connected IoT products.
One key factor in vulnerability is the timing sensitivity of the device’s operations. Systems that perform security checks over very short durations are particularly susceptible, as they leave narrow windows during which a glitch can cause a significant fault. If the device does not include timing redundancy or clock anomaly detection, attackers can exploit this behavior to gain unauthorized access.
Devices that lack internal clock generation and rely on external oscillators are also more exposed. If the attacker can gain physical access to the clock input line, they can inject glitches using relatively simple hardware. Even if the system uses an internal oscillator, external interference through test pads or shielding gaps may still allow clock manipulation.
Older or budget-constrained embedded systems may not include clock integrity checks, making them easier targets. Additionally, systems that boot directly into privileged modes or do not perform layered authentication checks are more likely to be compromised with a single glitch. Devices with debug interfaces that can be reactivated by corrupting the boot process are also attractive to attackers using clock glitching.
Real-World Use Cases of Clock Glitching
Several notable real-world applications of clock glitching demonstrate its effectiveness in bypassing otherwise robust protections. In the context of game console hacking, researchers have successfully used clock glitching to bypass digital signature checks, allowing the execution of custom or unauthorized code. These attacks have proven difficult to patch, as they exploit fundamental weaknesses in the system’s execution path.
In smartcard security, clock glitching has been used to extract cryptographic material by targeting the timing of signature generation or decryption routines. Since these operations often take place in hardware and rely on precisely timed instructions, injecting a fault during execution can cause the device to leak intermediate values or produce faulty outputs that can be analyzed to recover secret keys.
Another case involves bypassing secure boot protections in consumer electronics such as routers and set-top boxes. By glitching the clock during firmware verification, attackers have forced the system to accept unsigned or tampered firmware images. This has led to the development of persistent rootkits and custom firmware with elevated privileges.
Researchers have also demonstrated clock glitching against embedded medical devices, showcasing how vulnerabilities in timing control can lead to unauthorized access or function manipulation. This raises significant concerns in safety-critical applications, where device integrity and reliability are essential.
Mitigation Techniques Against Clock Glitching
Defending against clock glitching requires proactive design choices at both the hardware and firmware levels. One of the most effective defenses is the implementation of clock integrity checks. These circuits monitor the clock signal for unexpected frequency changes, glitches, or malformed edges. If any anomalies are detected, the system can halt execution, reset, or initiate tamper response procedures.
Another strategy is to use internal clock sources that are not easily influenced by external signals. Integrated oscillators are less accessible and more difficult to manipulate, reducing the likelihood of successful glitching. In systems that require external clocks, protective filters and signal conditioning components can help minimize susceptibility to injected glitches.
Redundant execution paths can also protect against clock glitching. By performing critical security checks more than once, in separate code paths or over multiple cycles, the system becomes more resistant to single-event faults. This makes it necessary for attackers to glitch multiple instructions successfully, greatly increasing the complexity and cost of the attack.
Software-based defenses include implementing randomized timing for sensitive operations. If critical functions do not execute at fixed intervals, attackers have a much harder time synchronizing glitch injections. While this does not eliminate the risk entirely, it adds a layer of uncertainty that complicates the attack process.
Code integrity checks, such as hash-based validation of runtime memory regions, can also detect the effects of glitching. If an instruction is skipped or corrupted, the resulting code path may deviate from the expected behavior. By monitoring for such deviations, the system can detect faults and respond accordingly.
Finally, physical shielding and tamper detection can help reduce the attack surface. Preventing access to the clock line and monitoring for physical intrusion discourages hardware-based attacks. These measures are especially important in devices deployed in untrusted or public environments.
Introduction to Reset Glitching in Fault Injection
Reset glitching is a fault injection technique that manipulates a device’s reset signal to trigger unintended or partially completed resets. Unlike power and clock glitching, which target timing and voltage characteristics during normal execution, reset glitching targets the device’s response to its reset condition. A typical reset line is used to reboot a device cleanly, reinitializing all internal states and bringing the system back to a known startup condition. However, if the reset signal is malformed, shortened, delayed, or corrupted, the system may fail to complete the initialization process, potentially leaving it in an insecure or unstable state.
In many embedded systems, a clean reset is crucial for establishing security parameters. It activates boot routines, security checks, and cryptographic verification mechanisms. When this process is disrupted by a glitch, parts of the initialization logic may be skipped, critical memory regions may not be cleared, or the device may boot into a legacy or debug mode unintentionally. This behavior can be exploited by attackers to gain access to privileged features, extract firmware, or bypass secure boot enforcement.
Reset glitching is considered more accessible than other forms of glitching because reset lines are often exposed or available through external interfaces. Many developers leave debug pins or reset headers exposed during manufacturing or testing, which makes the attack surface more reachable for hardware-level attackers. Although it may not offer the same precision as clock glitching, reset glitching can still be devastating when properly executed, especially on devices with poorly implemented boot protections.
How Reset Signals Work in Embedded Systems
In digital systems, the reset signal is a dedicated line connected to the microcontroller or system-on-chip that, when asserted, forces the device to restart and reinitialize all internal components. A typical reset event brings the system out of any undefined state, clears volatile memory, resets registers, and begins execution from the first instruction in firmware or ROM. The reset line is usually pulled high or low, depending on the design, and can be triggered manually via a button or programmatically by watchdog timers.
This reset procedure is essential for device stability and security. It ensures that no residual state from previous operations carries over into the new session. During reset, the system typically performs hardware tests, checks for secure boot conditions, and verifies firmware integrity. These steps are carefully sequenced to ensure the system is ready for trusted operation.
However, when a reset glitch is injected—typically by toggling the reset line for an extremely brief or improperly timed interval—the processor may only partially complete its reset sequence. This can result in an inconsistent system state where some subsystems are reinitialized while others retain their previous configurations. If the glitch occurs at a precise point, such as during bootloader verification or memory clearing, the system may skip those steps or fail to enforce security policies.
Some devices are designed to enter special boot or debug modes if they detect certain reset conditions. For example, holding a reset line low for a specific duration might signal the processor to enter a firmware update or diagnostics mode. If this logic can be manipulated through glitching, attackers may trick the device into granting access to features that are normally restricted.
Attack Scenarios Using Reset Glitching
Reset glitching can be used in a variety of attack scenarios, particularly when targeting devices with minimal reset filtering or when exploiting insecure bootloader designs. One common use case is triggering unintended access to boot ROM or firmware flashing interfaces. Many embedded systems include fallback boot modes that allow reprogramming firmware via USB, UART, or SPI when a specific reset condition is met. By crafting a reset glitch that mimics this condition, attackers can gain write or read access to protected memory regions.
Another use case involves skipping memory clearing operations. Upon reset, most systems are designed to wipe sensitive data from RAM or registers. A malformed reset pulse may fail to trigger these routines properly, leaving cryptographic keys, passwords, or session tokens in memory after reboot. By accessing this memory space immediately after a reset glitch, attackers can extract information that would otherwise be lost.
Reset glitching has also been used to interfere with signature validation during boot. If the system is designed to verify firmware signatures during a specific window after reset, a glitch at that moment may disrupt the verification, allowing unsigned code to be executed. In such cases, the device may assume the firmware is valid and proceed to boot malicious code, granting attackers full control.
Additionally, reset glitches have been shown to enable access to disabled or hidden debug features. Some microcontrollers and SoCs deactivate debugging interfaces such as JTAG or SWD after production, but re-enable them under certain reset conditions. By reproducing these conditions through glitching, attackers can gain privileged access to the internal workings of the chip, including secure memory and configuration registers.
Reset glitching is particularly effective against devices that lack tamper response mechanisms or that rely solely on boot-time checks for security. If the security model assumes that all checks are completed during reset and no faults occur afterward, then disrupting the reset process directly undermines the system’s entire trust foundation.
Tools and Methods for Performing Reset Glitching
Reset glitching requires less precision than other forms of fault injection but still demands careful control of timing and signal quality. The basic components of a reset glitching setup include a programmable glitcher circuit, a trigger mechanism to synchronize the glitch, and tools to monitor the device’s behavior in real-time.
A reset glitch can be generated using a simple microcontroller or transistor-based circuit capable of rapidly toggling the reset line. The attacker may first observe the device’s normal reset behavior using an oscilloscope or logic analyzer, then construct a waveform that mimics a clean reset but is shortened or malformed to disrupt execution. For finer control, glitching platforms offer programmable delay and pulse width features, allowing the attacker to adjust the glitch duration in sub-microsecond increments.
Triggering the glitch at the right moment is critical for success. This often involves identifying an external signal or event that indicates the start of a security-sensitive operation, such as the appearance of a boot message on a serial console or a voltage spike from a connected peripheral. Once this signal is detected, the glitch module sends the crafted reset pulse with a precisely calculated delay.
To monitor the effects of the glitch, attackers often use UART output, LED indicators, or other status signals from the target device. Repeated attempts with slight variations in glitch timing help narrow down the correct conditions for bypassing security. If the glitch causes the device to enter an unexpected state, produce abnormal output, or expose a previously unavailable interface, it is considered a successful fault injection.
Advanced attackers may combine reset glitching with other techniques, such as power analysis or electromagnetic fault injection, to improve timing accuracy or increase the range of exploitable conditions. For example, a side-channel trace might reveal the precise moment a key comparison is being performed, enabling more accurate glitch targeting.
Real-World Examples of Reset Glitching Attacks
Reset glitching has been successfully used in multiple real-world security assessments. In one well-documented case, researchers used a series of timed reset pulses to force a consumer-grade IoT device into firmware recovery mode. The mode, intended for factory use, allowed raw firmware extraction via a serial interface, exposing hardcoded credentials and encryption keys used by the manufacturer.
In another case, reset glitching was applied to a secure microcontroller in a payment terminal. The device was designed to erase its keys upon reset and disable debug interfaces. However, a glitch introduced during reset caused it to skip the key erasure routine, enabling attackers to recover sensitive data and clone the device’s identity. This attack highlighted the dangers of relying on reset logic for critical security enforcement.
Automotive systems have also been found vulnerable to reset glitching. In a demonstration involving an electronic control unit from a modern vehicle, researchers were able to bypass a locked bootloader by manipulating the reset signal. This allowed them to load custom firmware and take control of critical vehicle functions, revealing how reset glitches could be used as a stepping stone to broader vehicle exploitation.
Consumer electronics, including routers, set-top boxes, and smart displays, have also been compromised using reset glitching. Devices that rely on insecure boot sequences or expose update modes during reset are particularly vulnerable. In several cases, researchers gained root access to these systems by triggering recovery shells through malformed reset sequences.
Defending Systems Against Reset Glitching
Mitigating reset glitching requires a multi-layered approach that addresses both physical and logical vulnerabilities. One of the most effective defenses is implementing reset signal filtering. This can be achieved by using capacitive or resistive filtering circuits that smooth out short pulses and reject glitches below a certain duration threshold. By forcing the reset signal to meet strict timing requirements, these filters help prevent attackers from introducing malformed pulses.
Secure microcontrollers should include built-in reset detection logic that monitors the duration and shape of the reset pulse. If the reset does not match the expected profile, the device should ignore it or enter a safe error state. Additionally, hardware watchdogs can be configured to reset the device again if an incomplete initialization sequence is detected, ensuring that the system does not remain in a vulnerable state.
On the firmware side, designers should avoid relying solely on boot-time initialization to enforce security. Critical operations, such as memory clearing, key management, and signature verification, should be checked continuously or re-validated after each state transition. This ensures that even if a glitch occurs during reset, the system can detect inconsistencies and respond appropriately.
Disabling or locking debug interfaces before deployment is another crucial defense. Many reset glitching attacks rely on enabling legacy debug ports to access sensitive functionality. By permanently disabling these interfaces in production devices or requiring cryptographic authentication to enable them, manufacturers can greatly reduce the risk of exploitation.
Finally, physical access control remains an essential component of any secure system. Reset glitching requires direct or indirect access to the reset line, so securing the physical perimeter of the device, removing exposed test points, and covering or depopulating debug headers can all make attacks more difficult. For high-assurance systems, adding tamper sensors or active response mechanisms that erase data upon intrusion attempts can further protect against fault injection.
Conclusion
Reset glitching is a subtle yet powerful fault injection technique that takes advantage of incomplete or malformed resets to bypass security mechanisms in embedded systems. While it may seem simple compared to power or clock glitching, its effectiveness lies in its ability to corrupt the very process designed to enforce trust and integrity at boot. Devices that do not robustly handle reset events are at risk of being forced into insecure or exploitable states.
The widespread use of reset-based boot configurations, debug access triggers, and memory initialization routines creates ample opportunity for attackers who understand how to manipulate these signals. As demonstrated in various real-world cases, even a small glitch can lead to major compromises if the system is not properly secured.
Defending against reset glitching requires a combination of hardware signal integrity, secure firmware design, and physical tamper resistance. Developers and engineers must assume that adversaries will attempt to manipulate the reset process and must design their systems to detect and withstand such attempts. As fault injection techniques continue to evolve, ongoing testing, secure design practices, and awareness of low-level threats remain essential in protecting modern hardware systems.