CVE-2025-21871 addresses a vulnerability in the Linux kernel related to the OP-TEE supplicant, a user-space daemon responsible for handling communication between the OP-TEE Trusted Execution Environment (TEE) and client applications. The issue arises when the supplicant process is hung, crashed, or killed during the processing of an OP-TEE Remote Procedure Call (RPC). Specifically, improper shutdown ordering between the supplicant and the OP-TEE client application can cause the client process to wait indefinitely in the kernel for a supplicant response. This wait occurs in an unkillable state, leading to a system hang. The vulnerability manifests most notably during system reboot or shutdown sequences, where the supplicant's failure to respond causes the client to remain stuck, triggering the hung-task watchdog due to an endless wait loop rather than a normal uninterruptible wait. The fix implemented allows the client process to be killed even while waiting for the supplicant response, preventing indefinite blocking and system hang-ups that previously required a hard power cycle to recover. This vulnerability affects Linux kernel versions identified by the commit hash 4fb0a5eb364d239722e745c02aef0dbd4e0f1ad2, indicating a specific patch or kernel tree state. No known exploits are reported in the wild, and no CVSS score has been assigned yet. The vulnerability primarily impacts system availability and stability rather than confidentiality or integrity, as it leads to system hangs rather than unauthorized data access or modification.

For European organizations, the impact of CVE-2025-21871 centers on system availability and operational continuity. Organizations relying on Linux-based systems with OP-TEE support—commonly found in embedded devices, secure IoT gateways, and specialized industrial control systems—may experience system hangs during shutdown or reboot if the supplicant process fails. This can lead to unplanned downtime, increased maintenance costs, and potential disruption of critical services, especially in sectors such as manufacturing, telecommunications, and critical infrastructure where Linux and OP-TEE are used for secure operations. While the vulnerability does not directly expose sensitive data or allow privilege escalation, the forced hard power cycles to recover systems can cause hardware wear and increase the risk of data corruption or loss in transactional environments. Additionally, repeated system hangs could degrade trust in automated update or reboot processes, complicating patch management and incident response. The absence of known exploits reduces immediate risk, but the vulnerability's presence in kernel-level components means that any future exploitation could have widespread effects on system stability across affected devices.

To mitigate the risk posed by CVE-2025-21871, European organizations should: 1) Apply the official Linux kernel patches that address this issue as soon as they become available, ensuring that the OP-TEE supplicant and client interaction is properly handled to avoid indefinite waits. 2) Implement robust monitoring of system processes related to OP-TEE supplicant and client applications to detect hangs or crashes early, enabling proactive remediation before system-wide impact occurs. 3) Review and improve shutdown and reboot procedures to ensure correct ordering and graceful termination of supplicant and client processes, possibly incorporating custom scripts or systemd service dependencies to enforce proper sequencing. 4) For embedded and IoT devices, coordinate with hardware vendors to obtain updated firmware or kernel versions that include the fix, and plan for secure and timely deployment of these updates. 5) Establish fallback mechanisms such as watchdog timers or remote management capabilities that can safely recover hung systems without requiring hard power cycles, minimizing operational disruption. 6) Conduct thorough testing of updates in staging environments that replicate production conditions to verify that the fix resolves the issue without introducing regressions.