Description
In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix NULL pointer dereference in module event cache removal

A module-only event filter such as ":mod:foo" is cached with a NULL
event_mod->match when foo has not been loaded. If a later write tries to
remove a specific match from the same module, remove_cache_mod() passes
the NULL cached match to strcmp(), causing a NULL pointer dereference.

The issue can be reproduced from userspace:

echo ':mod:trace_events_kunit_missing' > /sys/kernel/tracing/set_event
echo '!foo_bar:mod:trace_events_kunit_missing' >> /sys/kernel/tracing/set_event

The second write must be a concatenation (">>") to not include O_TRUNC as
that would cause ftrace_clear_events() to clear the cached modules lines.

The crash was reproduced on x86_64 QEMU while KUnit workers contended on
the event tracing path:

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
RIP: 0010:strcmp+0x10/0x30
Call Trace:
__ftrace_set_clr_event_nolock+0x373/0x4a0
ftrace_set_clr_event+0xf0/0x180
ftrace_event_write+0xdf/0x110
vfs_write+0xf6/0x440
ksys_write+0x68/0xe0
do_syscall_64+0xf9/0x540
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Check event_mod->match before comparing it, consistent with the existing
NULL checks for the cached system and event fields. The mismatched removal
continues to return -EINVAL; a broad cached module filter is removed with
"!:mod:<module>".
Published: 2026-08-22
Score: n/a
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

The vulnerability originates from a NULL pointer dereference in the kernel’s tracing subsystem when a module‑only event filter is removed from the cache. Triggering the error causes the Linux kernel to crash and reboot, disrupting system availability for all processes including privileged services. Because the fault occurs within the core kernel, it does not provide an attacker with direct code execution or privilege escalation; the impact is strictly limited to denial of service.

Affected Systems

All Linux kernel releases that contain the unfixed tracing code are affected. The exact version range is not specified, but the issue was present in kernels that had a module‑only event filter causing a NULL cached match when the module was not loaded. The fix applies broadly across Linux distributions, so any distribution using a kernel older than the patch contains the flaw.

Risk and Exploitability

The EPSS score is currently unavailable and the vulnerability is not listed in the CISA KEV catalog, suggesting no widespread exploit activity yet. However, the attack vector requires write access to /sys/kernel/tracing/set_event, which is typically restricted to privileged users. If an attacker can obtain such access, they can easily reproduce the crash by echoing a malformed filter into the file. Given the lack of a CVSS score, the severity cannot be quantified precisely, but the confirmed kernel panic indicates a high impact on availability.

Generated by OpenCVE AI on August 22, 2026 at 18:35 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Apply the latest Linux kernel update that includes the tracing NULL‑pointer fix.
  • Limit write permissions to /sys/kernel/tracing/set_event to privileged users only.
  • If tracing is not required, disable the ftrace subsystem or monitor kernel logs for event‑related crashes.

Generated by OpenCVE AI on August 22, 2026 at 18:35 UTC.

Tracking

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Advisories

No advisories yet.

History

Sat, 22 Aug 2026 19:00:00 +0000

Type Values Removed Values Added
Weaknesses CWE-476

Sat, 22 Aug 2026 15:45:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: tracing: Fix NULL pointer dereference in module event cache removal A module-only event filter such as ":mod:foo" is cached with a NULL event_mod->match when foo has not been loaded. If a later write tries to remove a specific match from the same module, remove_cache_mod() passes the NULL cached match to strcmp(), causing a NULL pointer dereference. The issue can be reproduced from userspace: echo ':mod:trace_events_kunit_missing' > /sys/kernel/tracing/set_event echo '!foo_bar:mod:trace_events_kunit_missing' >> /sys/kernel/tracing/set_event The second write must be a concatenation (">>") to not include O_TRUNC as that would cause ftrace_clear_events() to clear the cached modules lines. The crash was reproduced on x86_64 QEMU while KUnit workers contended on the event tracing path: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode RIP: 0010:strcmp+0x10/0x30 Call Trace: __ftrace_set_clr_event_nolock+0x373/0x4a0 ftrace_set_clr_event+0xf0/0x180 ftrace_event_write+0xdf/0x110 vfs_write+0xf6/0x440 ksys_write+0x68/0xe0 do_syscall_64+0xf9/0x540 entry_SYSCALL_64_after_hwframe+0x77/0x7f Check event_mod->match before comparing it, consistent with the existing NULL checks for the cached system and event fields. The mismatched removal continues to return -EINVAL; a broad cached module filter is removed with "!:mod:<module>".
Title tracing: Fix NULL pointer dereference in module event cache removal
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-08-22T15:32:13.808Z

Reserved: 2026-08-15T05:44:03.922Z

Link: CVE-2026-74633

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-08-22T16:16:36.380

Modified: 2026-08-22T16:16:36.380

Link: CVE-2026-74633

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-22T18:45:04Z

Weaknesses