CVE-2020-25860 in RAUC Update Client
Summary
by MITRE • 12/21/2020
The install.c module in the Pengutronix RAUC update client prior to version 1.5 has a Time-of-Check Time-of-Use vulnerability, where signature verification on an update file takes place before the file is reopened for installation. An attacker who can modify the update file just before it is reopened can install arbitrary code on the device.
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Analysis
by VulDB Data Team • 05/26/2026
The vulnerability described in the Pengutronix RAUC update client represents a critical time-of-check time-of-use flaw that fundamentally undermines the security of the update mechanism. This issue affects versions prior to 1.5 and demonstrates a classic race condition where the system performs signature verification on an update file before the file is actually reopened for installation. The flaw creates a window of opportunity for attackers to manipulate the update file between the verification phase and the installation phase, effectively bypassing the integrity checks that should protect against malicious modifications.
The technical implementation of this vulnerability stems from the sequential nature of the update process where the system first validates the digital signature of an update file and then reopens the same file for actual installation. During this gap between signature verification and file reopening, an attacker with access to modify the update file can substitute the legitimate content with malicious code. This approach exploits the fundamental principle that security checks should be performed on the final, unmodified state of the file rather than on a potentially altered version that will be processed later. The vulnerability aligns with CWE-367, which specifically addresses time-of-check to time-of-use flaws, and represents a clear violation of the principle of least privilege and secure file handling practices.
The operational impact of this vulnerability extends far beyond simple code execution, as it provides attackers with a pathway to compromise entire embedded systems through what should be a trusted update mechanism. In embedded environments where RAUC is commonly deployed, such as industrial control systems, IoT devices, or automotive applications, this vulnerability could enable attackers to gain persistent control over critical infrastructure. The attack scenario involves an attacker who can modify the update file at any point between signature verification and installation, potentially leading to full system compromise through privilege escalation, data exfiltration, or denial of service conditions. This vulnerability directly maps to ATT&CK technique T1070.004, which covers "Indicator Removal on Host: File Deletion," as attackers could potentially use this vulnerability to not only install malicious code but also to remove or alter system files.
Mitigation strategies for this vulnerability must address both the immediate flaw in the RAUC implementation and broader security practices for update mechanisms. The primary fix involves ensuring that signature verification occurs on the same file instance that will be installed, eliminating the time-of-check to time-of-use window. This can be achieved through either reusing the same file handle throughout the process or by performing verification on a copy of the file that cannot be modified by external processes. Additionally, implementing proper file system permissions and access controls can help prevent unauthorized modifications during the installation window. Organizations should also consider implementing secure update protocols that include cryptographic checksums, tamper-evident packaging, and continuous monitoring of update processes. The vulnerability highlights the importance of following secure coding practices such as those outlined in the OWASP Secure Coding Practices and emphasizes the need for comprehensive testing of update mechanisms under various threat scenarios.