CVE-2026-74633
Received Received - Intake

NULL Pointer Dereference in Linux Kernel Tracing

Publication date: 2026-08-22

Last updated on: 2026-08-22

Assigner: kernel.org

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>".

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Meta Information

Published
2026-08-22
Last Modified
2026-08-22
Generated
2026-08-22
AI Q&A
2026-08-22
EPSS Evaluated
N/A
NVD
CVE-2026-74633
EUVD
EUVD-2026-64570

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This is a NULL pointer dereference vulnerability in the Linux kernel's tracing subsystem. It occurs when a module-only event filter like ':mod:foo' is cached with a NULL match if the module hasn't been loaded. Later removal attempts pass this NULL match to strcmp(), causing a kernel crash.

Detection Guidance

The vulnerability can be reproduced by running these commands on a vulnerable system: echo ':mod:trace_events_kunit_missing' > /sys/kernel/tracing/set_event and then echo '!foo_bar:mod:trace_events_kunit_missing' >> /sys/kernel/tracing/set_event. A crash would indicate the presence of this issue.

Impact Analysis

This vulnerability can cause a kernel crash (NULL pointer dereference) when specific tracing commands are executed from userspace. This leads to system instability or denial of service. Attackers with local access could trigger this to crash the system.

Mitigation Strategies

Apply the Linux kernel patch that fixes the NULL pointer dereference in module event cache removal. The fix involves checking event_mod->match before comparison in the tracing subsystem.

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