Severity
High
Analysis Summary
A publicly available proof-of-concept (PoC) exploit has increased the risk associated with CVE-2025-38352, a race condition vulnerability in the Linux kernel’s POSIX CPU timer implementation. The flaw exists in the handle_posix_cpu_timers() function, which is responsible for processing CPU timer signals during scheduler ticks. Due to improper synchronization, attackers can trigger a use-after-free (UAF) condition in kernel memory, potentially leading to local privilege escalation and full system compromise.
The vulnerability arises from a timing gap between when the kernel collects expired POSIX CPU timers and when it later processes them. An attacker can exploit this window by freeing a timer object while it is still being referenced by the kernel. Successful exploitation requires specific conditions, including forcing a thread into a zombie process state and carefully coordinating timer deletion during active timer handling. The issue primarily affects systems where CONFIG_POSIX_CPU_TIMERS_TASK_WORK is disabled, making 32-bit Android kernels and certain embedded Linux systems especially vulnerable.
The PoC, published on GitHub by security researcher, demonstrates a practical exploitation chain. The exploit creates a POSIX CPU timer, forces a task into a zombie state, reaps the task during timer processing, and deletes the timer using the timer_delete() syscall. This sequence causes premature deallocation of the timer structure, which the kernel continues to access, resulting in a UAF condition. On KASAN-enabled systems, this triggers memory sanitizer warnings related to UAF writes in posix_timer_queue_signal(), while non-KASAN systems may exhibit kernel warnings in send_sigqueue().
Security advisories indicate that CVE-2025-38352 has already been exploited in limited, targeted attacks, increasing its severity despite requiring local access and precise timing. Linux kernel maintainers have released patches across stable branches that eliminate the race condition by preventing zombie processes from executing timer handling code. Administrators and usersparticularly those managing Android and embedded Linux devicesare strongly advised to apply updates immediately, as the public availability of the PoC significantly shortens the exploitation window for unpatched systems.
Impact
- Gain Access
- Privilege Escalation
Indicators of Compromise
CVE
CVE-2025-38352
Affected Vendors
Remediation
- Apply kernel security patches immediately by upgrading to the latest Linux kernel versions released through the stable branches that address CVE-2025-38352.
- Update Android and embedded Linux devices to vendor-provided security updates, with priority given to 32-bit Android kernels where the risk is higher.
- Enable CONFIG_POSIX_CPU_TIMERS_TASK_WORK where feasible, as the vulnerability primarily affects systems with this option disabled.
- Restrict local user access on affected systems to reduce the likelihood of exploitation, since the attack requires local execution.
- Harden system configurations by limiting untrusted applications and enforcing least-privilege principles for user accounts and processes.
- Monitor kernel logs and security alerts for KASAN warnings or unusual kernel messages related to POSIX timers, such as errors in posix_timer_queue_signal() or send_sigqueue().
- Use kernel hardening and security features (e.g., SELinux, AppArmor, and KASAN in testing environments) to detect or mitigate exploitation attempts.
- Conduct regular vulnerability management and patch audits to ensure no systems remain on vulnerable kernel versions after the PoC release.