Improper Update of Reference Count Affecting perf6.18-debuginfo package, versions <1:6.18.20-20.229.amzn2023


Severity

Recommended
high

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
0.02% (5th percentile)

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  • Snyk IDSNYK-AMZN2023-PERF618DEBUGINFO-16348323
  • published3 May 2026
  • disclosed18 Mar 2026

Introduced: 18 Mar 2026

CVE-2026-23248  (opens in a new tab)
CWE-911  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 perf6.18-debuginfo to version 1:6.18.20-20.229.amzn2023 or higher.
This issue was patched in ALAS2023-2026-1596.

NVD Description

Note: Versions mentioned in the description apply only to the upstream perf6.18-debuginfo package and not the perf6.18-debuginfo package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.

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

perf/core: Fix refcount bug and potential UAF in perf_mmap

Syzkaller reported a refcount_t: addition on 0; use-after-free warning in perf_mmap.

The issue is caused by a race condition between a failing mmap() setup and a concurrent mmap() on a dependent event (e.g., using output redirection).

In perf_mmap(), the ring_buffer (rb) is allocated and assigned to event->rb with the mmap_mutex held. The mutex is then released to perform map_range().

If map_range() fails, perf_mmap_close() is called to clean up. However, since the mutex was dropped, another thread attaching to this event (via inherited events or output redirection) can acquire the mutex, observe the valid event->rb pointer, and attempt to increment its reference count. If the cleanup path has already dropped the reference count to zero, this results in a use-after-free or refcount saturation warning.

Fix this by extending the scope of mmap_mutex to cover the map_range() call. This ensures that the ring buffer initialization and mapping (or cleanup on failure) happens atomically effectively, preventing other threads from accessing a half-initialized or dying ring buffer.

CVSS Base Scores

version 3.1