Linux Kernel POSIX CPU Timers Race Condition Vulnerability (CVE-2025-38352) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTLinux kernel deployments where CONFIG_POSIX_CPU_TIMERS_TASK_WORK is disabled or not supported
Local attackers can exploit a race condition to trigger a kernel panic (DoS) or potentially achieve Local Privilege Escalation (LPE) via memory corruption
Apply the official stable kernel patches or ensure CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y is enabled in the kernel configuration
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrade your Linux kernel to the latest stable release provided by your distribution vendor to apply the upstream fixes.
# For Debian/Ubuntu-based systems
sudo apt-get update && sudo apt-get install --only-upgrade -y linux-image-generic
# For RHEL/Rocky Linux/AlmaLinux-based systems
sudo dnf clean all && sudo dnf update -y kernel
# Reboot the system to apply the new kernel
sudo reboot2. Temporary Workaround & Hardening Configuration
Verify if your current kernel configuration has CONFIG_POSIX_CPU_TIMERS_TASK_WORK enabled. If enabled, exit_task_work() runs before exit_notify(), preventing the race condition entirely.
# Check kernel configuration for the mitigation flag
zgrep 'CONFIG_POSIX_CPU_TIMERS_TASK_WORK' /proc/config.gz || grep 'CONFIG_POSIX_CPU_TIMERS_TASK_WORK' /boot/config-$(uname -r)3. Log Audit & IoC Verification Commands
Audit system logs and kernel ring buffers for anomalies related to POSIX CPU timers or unexpected kernel panics.
# Search kernel logs for related function calls and faults
sudo dmesg -T | grep -Ei 'posix_cpu_timer|handle_posix_cpu_timers|general protection fault'
sudo journalctl -k --grep='posix_cpu_timer'Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2025-38352) is a race condition (CWE-367) within the POSIX CPU timers subsystem of the Linux kernel. When an exiting, non-autoreaping task passes the exit_notify() phase and invokes handle_posix_cpu_timers() from an interrupt (IRQ) context, it becomes susceptible to being reaped by its parent process or a debugger immediately after releasing the task lock via unlock_task_sighand().
2. Exploitation Mechanics & Attack Scenario
If a concurrent execution of posix_cpu_timer_del() occurs at this exact moment, the deletion routine attempts to verify if the timer is currently firing (timer->it.cpu.firing != 0). However, because the target task has already been reaped, helper functions such as cpu_timer_task_rcu() and/or lock_task_sighand() will fail. This failure prevents the kernel from detecting the active state of the timer, leading to inconsistent state tracking, potential Use-After-Free (UAF) conditions, or null pointer dereferences.
3. Infrastructure & Business Impact
An exploit targeting this vulnerability allows a local unprivileged user to crash the operating system, resulting in a complete Denial of Service (DoS) for all hosted workloads. In high-security environments, sophisticated local attackers could leverage the resulting memory corruption to manipulate kernel space structures, potentially escalating privileges to root and compromising the entire infrastructure.
Official Vendor Advisories & References
In the Linux kernel, the following vulnerability has been resolved: posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del() If an exiting non-autoreaping task has already passed exit_notify() and calls handle_posix_cpu_timers() from IRQ, it can be reaped by its parent or debugger right after unlock_task_sighand(). If a concurrent posix_cpu_timer_del() runs at that moment, it won't be able to detect timer->it.cpu.firing != 0: cpu_timer_task_rcu() and/or lock_task_sighand() will fail. Add the tsk->exit_state check into run_posix_cpu_timers() to fix this. This fix is not needed if CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y, because exit_task_work() is called before exit_notify(). But the check still makes sense, task_work_add(&tsk->posix_cputimers_work.work) will fail anyway in this case.
Frequently Asked SecOps Questions (CVE-2025-38352)
FAQQ1. How critical is CVE-2025-38352 and is it actively exploited in the wild?
CVE-2025-38352 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 1.4%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2025-38352?
Primary impacted vendors include linux across linux_kernel. Scope summary: All Linux kernel versions vulnerable when compiled without CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y
Q3. What temporary mitigations or workarounds exist for CVE-2025-38352 before patching?
[Mitigation] Apply the official stable kernel patches or ensure CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y is enabled in the kernel configuration Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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