CVE-2026-74633

tracing: Fix NULL pointer dereference in module event cache removal

Published Aug 22, 2026 CVSS 3.1 · 5.5 Medium EPSS < 1% KEV · Not listed

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>".

Analysis

Technical 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 < 1% and the vulnerability is not listed in the CISA KEV catalog, suggesting limited exploitation activity. 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. The CVSS score of 5.5 indicates a medium severity, but the confirmed kernel panic indicates a high impact on availability.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`b355247df104ef6644288884afd2c08b7bf49897`	affected	< 152a00440dc6ef62c6e4cf9bd881a7e6bb81fda9
`b355247df104ef6644288884afd2c08b7bf49897`	affected	< ad4e9dd5fec7a322a471ff36fb9c76214e3c6992
`b355247df104ef6644288884afd2c08b7bf49897`	affected	< b69859204d4db3acd86c1c2dadcef0d77b451933

Linux

affected

Version	Status	Constraints
`6.14`	affected	—
`0`	unaffected	< 6.14
`6.18.45`	unaffected	≤ 6.18.*
`7.1.9`	unaffected	≤ 7.1.*
`7.2`	unaffected	≤ *

No data.

Vendor Product Versions

Linux

Linux Kernel

Version	Status	Scheme	Platform
`[b355247df104ef6644288884afd2c08b7bf49897,152a00440dc6ef62c6e4cf9bd881a7e6bb81fda9)`	affected	code_commit	—
`[b355247df104ef6644288884afd2c08b7bf49897,ad4e9dd5fec7a322a471ff36fb9c76214e3c6992)`	affected	code_commit	—
`[b355247df104ef6644288884afd2c08b7bf49897,b69859204d4db3acd86c1c2dadcef0d77b451933)`	affected	code_commit	—

Linux

Linux Kernel

Version	Status	Scheme	Platform
`6.14`	affected	generic	—
`[0,6.14)`	unaffected	generic	—
`[6.18.45,6.18.*]`	unaffected	generic	—
`[7.1.9,7.1.*]`	unaffected	generic	—
`[7.2,*]`	unaffected	generic	—

Remediation

No solution or workaround provided in the CVE record.

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 25, 2026 at 13:39 UTC.

Tracking

Advisories

Source	ID	Title
Ubuntu USN	USN-9019-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-9020-1	Linux kernel vulnerabilities

Metrics

No CVSS v4.0

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.166% probability within 30 days)

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/stable/c/152a00440dc6ef62c6e4cf9bd881a7e6bb81fda9
https://git.kernel.org/stable/c/ad4e9dd5fec7a322a471ff36fb9c76214e3c6992
https://git.kernel.org/stable/c/b69859204d4db3acd86c1c2dadcef0d77b451933
https://lore.kernel.org/linux-cve-announce/2026082222-CVE-2026-74633-6b87@gregkh/T
https://nvd.nist.gov/vuln/detail/CVE-2026-74633
https://www.cve.org/CVERecord?id=CVE-2026-74633

History

Aug 25, 2026 12:15 PM Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
References		https://lore.kernel.org/linux-cve-announce/2026082222-CVE-2026-74633-6b87@gregkh/T https://nvd.nist.gov/vuln/detail/CVE-2026-74633 https://www.cve.org/CVERecord?id=CVE-2026-74633
Metrics	threat_severity `None`	cvssV3_1 `{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}` threat_severity `Low`

Aug 22, 2026 7:00 PM Weaknesses updated View changes

Type	Values Removed	Values Added
Weaknesses		CWE-476

Aug 22, 2026 3:45 PM Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references View changes

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		https://git.kernel.org/stable/c/152a00440dc6ef62c6e4cf9bd881a7e6bb81fda9 https://git.kernel.org/stable/c/ad4e9dd5fec7a322a471ff36fb9c76214e3c6992 https://git.kernel.org/stable/c/b69859204d4db3acd86c1c2dadcef0d77b451933