CVE-2017-18347 in STM32F0
Summary
by MITRE
Incorrect access control in RDP Level 1 on STMicroelectronics STM32F0 series devices allows physically present attackers to extract the device's protected firmware via a special sequence of Serial Wire Debug (SWD) commands because there is a race condition between full initialization of the SWD interface and the setup of flash protection.
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Analysis
by VulDB Data Team • 03/23/2020
The vulnerability CVE-2017-18347 represents a critical access control flaw in RDP Level 1 protection mechanisms of STMicroelectronics STM32F0 series microcontrollers. This issue affects devices that implement the Read-Out Protection (RDP) feature designed to prevent unauthorized access to protected firmware. The vulnerability specifically targets the physical security model of these microcontrollers, where an attacker with physical access can exploit a timing race condition to bypass the intended protection measures. The flaw exists in the implementation of the Serial Wire Debug (SWD) interface initialization sequence, creating a window of opportunity for unauthorized firmware extraction.
The technical root cause of this vulnerability stems from a race condition between two critical processes within the device's boot sequence. During the normal operation, the SWD interface undergoes full initialization while simultaneously the flash memory protection mechanisms are being configured. This concurrent execution creates a temporal gap where the device's protection mechanisms are not yet fully active, but the SWD interface is already operational and accessible. The vulnerability manifests when an attacker can execute a carefully orchestrated sequence of SWD commands that takes advantage of this initialization timing window. According to CWE-362, this represents a race condition vulnerability where the security of the system depends on the timing of operations, making it particularly challenging to detect and mitigate through conventional means.
The operational impact of this vulnerability is severe for embedded systems utilizing STM32F0 series devices, as it completely undermines the intended Read-Out Protection mechanism. Attackers with physical access can extract the entire firmware image, potentially exposing sensitive cryptographic keys, proprietary algorithms, and confidential application logic. This compromises the integrity and confidentiality of the embedded system, making it vulnerable to reverse engineering and subsequent attacks. The vulnerability affects devices that rely on RDP Level 1 protection, which is designed to prevent unauthorized firmware access but fails due to the timing flaw in the SWD initialization sequence. This creates a security boundary failure where the physical security model is bypassed, allowing attackers to perform firmware extraction without proper authorization.
The attack vector for this vulnerability requires physical presence and specialized knowledge of the SWD protocol, making it suitable for targeted attacks against embedded systems in secure environments. The attack typically involves a sequence of SWD commands that must be executed with precise timing to exploit the race condition. This aligns with ATT&CK technique T1059.001, where attackers leverage physical access to execute commands through debugging interfaces. The vulnerability affects a wide range of automotive, industrial, and IoT applications that use STM32F0 series microcontrollers, where the extracted firmware can reveal critical system information and potentially enable further attacks against connected networks. Security professionals should note that this vulnerability cannot be mitigated through software updates or configuration changes, as it resides in the hardware implementation of the device's protection mechanisms.
Mitigation strategies for CVE-2017-18347 are limited due to the hardware-level nature of the vulnerability. The most effective approaches include implementing additional physical security measures such as tamper-evident packaging, secure boot mechanisms, and hardware-based encryption for sensitive data storage. Organizations should consider replacing affected devices with newer microcontroller models that have corrected implementations of the RDP protection mechanisms. The vulnerability highlights the importance of considering timing attacks and race conditions in hardware security designs, particularly in critical embedded systems where physical access is possible. Security architects should also implement network-level protections and monitoring to detect potential firmware extraction attempts, even though the root cause cannot be fully addressed through software means. This vulnerability serves as a reminder of the critical importance of thorough security testing of hardware protection mechanisms, particularly those relying on timing-sensitive operations.