CVE-2026-68146: Linux Kernel Race Condition Vulnerability

CVE-2026-68146 Overview

CVE-2026-68146 is a race condition vulnerability in the Linux kernel's ftrace subsystem. The flaw affects the trace_parser structure, which is allocated when a trace file is opened and shared across write and release handlers. When userspace shares a trace file descriptor across multiple threads, concurrent write calls race on the parser's internal idx, cont, and buffer fields. This results in corrupted parser input or undefined behavior within the kernel. The upstream fix introduces a global mutex, parser_lock, to serialize access to trace_parser across write and release paths.

Critical Impact
Concurrent writes to a shared ftrace file descriptor can corrupt kernel parser state, producing undefined behavior in ftrace_regex_* and ftrace_graph_* handlers.

Affected Products

Linux kernel (ftrace subsystem)
Stable kernel branches referenced by upstream commits 3d0dd13, 65bf73b, 7720b63, 90be137, and e807c91
Distributions shipping vulnerable kernel versions prior to the fix

Discovery Timeline

2026-08-10 - CVE-2026-68146 published to NVD
2026-08-10 - Last updated in NVD database

Technical Details for CVE-2026-68146

Vulnerability Analysis

The vulnerability resides in the ftrace tracing infrastructure of the Linux kernel. Ftrace exposes a set of trace files that userspace opens to configure kernel tracing. When a process opens one of these files, the kernel allocates a trace_parser structure to parse subsequent write input.

The affected handler paths include the open functions ftrace_regex_open() and ftrace_graph_open(), the write functions ftrace_regex_write() and ftrace_graph_write(), and the release functions ftrace_regex_release() and ftrace_graph_release(). The parser is intended to be used sequentially by a single writer.

If userspace shares a file descriptor across multiple threads, those threads can invoke write() simultaneously. The write handlers concurrently mutate the same parser instance, causing the idx, cont, and buffer fields to drift into inconsistent states.

Root Cause

The root cause is a missing synchronization primitive around shared parser state [Race Condition]. The trace_parser structure was designed under the assumption of single-threaded access per file descriptor, but the kernel did not enforce this invariant. Concurrent updates to the parser index and buffer produce corrupted parses and may lead to undefined kernel behavior.

Attack Vector

A local user with permission to open ftrace files can trigger the race. The user opens a trace file, duplicates or shares the resulting file descriptor across multiple threads, and issues concurrent write() calls. No remote vector applies because ftrace files are local kernel interfaces exposed through tracefs or debugfs. Impact centers on kernel state corruption rather than a directly weaponizable memory-safety primitive, but undefined behavior in tracing paths can affect system stability.

The upstream fix adds a global parser_lock mutex acquired in all write and release paths to serialize access. See the patches in the kernel.org stable tree for the exact changes.

Detection Methods for CVE-2026-68146

Indicators of Compromise

Kernel warnings or oops messages originating from ftrace_regex_write or ftrace_graph_write call sites
Unexpected tracing configuration changes on hosts where ftrace is used for observability
Multiple threads within a single process concurrently writing to the same tracefs file descriptor

Detection Strategies

Audit kernel version banners against fixed commits 3d0dd138, 65bf73be, 7720b63b, 90be1378, and e807c919
Monitor dmesg for anomalous ftrace-related traces or parser errors on production hosts
Use auditd rules to record openat and write syscalls against /sys/kernel/tracing and /sys/kernel/debug/tracing paths

Monitoring Recommendations

Alert on non-root processes accessing tracefs or debugfs interfaces
Track kernel crash telemetry and correlate with recent ftrace usage
Baseline expected consumers of ftrace (for example, perf, trace-cmd) and flag unexpected callers

How to Mitigate CVE-2026-68146

Immediate Actions Required

Apply the upstream stable kernel updates that include the parser_lock serialization fix
Restrict access to tracefs and debugfs to trusted administrators only
Inventory hosts running affected kernel versions and prioritize patch deployment

Patch Information

The fix is available in the Linux stable tree via commits 3d0dd13, 65bf73b, 7720b63, 90be137, and e807c91. Rebuild or update to a distribution kernel that incorporates these patches.

Workarounds

Mount tracefs and debugfs with restrictive permissions and ensure only privileged users can read or write trace files
Disable tracefs and debugfs on production systems that do not require kernel tracing
Use kernel lockdown mode where applicable to limit tracing interfaces

bash

# Restrict tracefs access to root only
mount -o remount,mode=0700 /sys/kernel/tracing
chmod 700 /sys/kernel/debug/tracing

# Verify running kernel version against fixed commits
uname -r