CVE-2026-23106: Linux Kernel Privilege Escalation Flaw

CVE-2026-23106 Overview

A race condition vulnerability has been identified in the Linux kernel's timekeeping subsystem. The vulnerability exists in the __do_adjtimex() function, which was introduced to handle adjtimex for any timekeeper but contains an incorrect reference to tk_core that was not properly updated. When called on an auxiliary timekeeper, this flaw causes the core timekeeper to be updated incorrectly, potentially leading to system instability or denial of service conditions.

Critical Impact

This vulnerability allows incorrect modification of the core timekeeper's sequence lock without holding its associated spinlock, triggering lock debugging warnings and potentially causing timing inconsistencies in the kernel.

Affected Products

• Linux kernel (versions with affected timekeeping subsystem)

Discovery Timeline

• 2026-02-04 - CVE CVE-2026-23106 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-23106

Vulnerability Analysis

The vulnerability resides in the kernel's timekeeping implementation, specifically in how __do_adjtimex() handles auxiliary timekeepers. When this function was introduced to provide a unified interface for adjusting any timekeeper, a reference to tk_core was inadvertently left unchanged. This creates a situation where operations intended for an auxiliary timekeeper incorrectly modify the core timekeeper instead.

The issue manifests as a race condition because the code writes to the timekeeper's sequence lock without first acquiring the required spinlock. This violates the locking invariants expected by the kernel's seqlock implementation and is caught by the kernel's lock debugging diagnostics.

Root Cause

The root cause is an incorrect reference in __do_adjtimex() located in kernel/time/timekeeping.c. When the function was designed to handle adjtimex operations for any timekeeper (including auxiliary timekeepers), the hardcoded reference to tk_core was not updated to use the appropriate timekeeper passed to the function. This results in the wrong timekeeper's state being modified during aux_clock_adj operations.

Attack Vector

The vulnerability can be triggered through the clock_adjtime syscall when operating on auxiliary clocks. The attack path follows this flow:

1. A user-space process calls clock_adjtime() targeting an auxiliary clock
2. The kernel invokes __do_sys_clock_adjtime() in kernel/time/posix-timers.c
3. This calls aux_clock_adj() which triggers __do_adjtimex()
4. Due to the bug, the core timekeeper (tk_core) is modified instead of the auxiliary timekeeper
5. The sequence lock write occurs without proper spinlock protection

The kernel's lock debugging mechanism detects this violation and generates a warning:

WARNING: include/linux/seqlock.h:226 at __do_adjtimex+0x394/0x3b0

Detection Methods for CVE-2026-23106

Indicators of Compromise

• Kernel warning messages containing WARNING: include/linux/seqlock.h:226 at __do_adjtimex
• Log entries showing aux_clock_adj stack traces from kernel/time/timekeeping.c
• System time anomalies or unexpected clock behavior after auxiliary clock adjustments
• Kernel lockdep warnings related to timekeeping spinlock operations

Detection Strategies

• Monitor kernel logs (dmesg) for seqlock-related warnings in the timekeeping subsystem
• Implement system monitoring to detect unusual clock drift or timing inconsistencies
• Deploy SentinelOne Singularity Platform for real-time kernel anomaly detection
• Enable kernel lock debugging (CONFIG_DEBUG_LOCK_ALLOC) to catch lock ordering violations

Monitoring Recommendations

• Configure syslog aggregation to capture and alert on timekeeping-related kernel warnings
• Monitor for processes making frequent clock_adjtime syscalls on auxiliary clocks
• Implement kernel-level monitoring for sequence lock violations in critical subsystems
• Use SentinelOne's kernel-level telemetry to detect abnormal timekeeping behavior

How to Mitigate CVE-2026-23106

Immediate Actions Required

• Apply the official kernel patches to affected systems as soon as available
• Review systems for signs of exploitation by checking kernel logs for related warnings
• Consider temporarily restricting access to clock_adjtime syscall if auxiliary clock adjustments are not required
• Update to a patched kernel version when available from your distribution

Patch Information

The Linux kernel developers have released patches to address this vulnerability. The fix ensures that __do_adjtimex() correctly updates the auxiliary timekeeper rather than incorrectly modifying tk_core. The patches are available in the kernel stable tree:

• Kernel Git Commit 8f7c9db
• Kernel Git Commit e806f7d

Workarounds

• Limit user access to auxiliary clock adjustment capabilities using seccomp or AppArmor profiles
• Audit applications that use clock_adjtime on auxiliary clocks and restrict their execution where possible
• Enable enhanced kernel lock debugging to detect exploitation attempts
• Consider using SentinelOne's application control features to restrict untrusted processes from making timekeeping syscalls

# Check current kernel version for patch status
uname -r

# Monitor for exploitation attempts in kernel logs
dmesg | grep -E "(seqlock|__do_adjtimex|aux_clock_adj)"

# Review recent clock_adjtime syscalls (requires auditd)
ausearch -sc clock_adjtime