---
id: CVE-2026-23248
title: 'perf/core: Fix refcount bug and potential UAF in perf_mmap'
summary: |-
  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…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= b709eb872e19a19607bbb6d2975bc264d59735cf <
    c27dea9f50ed525facb62ef647dddc4722456e07
  - >-
    Linux >= b709eb872e19a19607bbb6d2975bc264d59735cf <
    ac7ecb65af170a7fc193e7bd8be15dac84ec6a56
  - >-
    Linux >= b709eb872e19a19607bbb6d2975bc264d59735cf <
    77de62ad3de3967818c3dbe656b7336ebee461d2
  - Linux 6.14
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T15:06:58.307161Z'
published: '2026-03-18'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:09:51.119Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-23248'
references:
  - url: 'https://git.kernel.org/stable/c/c27dea9f50ed525facb62ef647dddc4722456e07'
  - url: 'https://git.kernel.org/stable/c/ac7ecb65af170a7fc193e7bd8be15dac84ec6a56'
  - url: 'https://git.kernel.org/stable/c/77de62ad3de3967818c3dbe656b7336ebee461d2'
tags:
  - cve.org
epss: 0.00124
epssPercentile: 0.01928
ingestedAt: '2026-10-16T17:24:46.642Z'
---

## Overview

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.

## Affected

- `Linux >= b709eb872e19a19607bbb6d2975bc264d59735cf < c27dea9f50ed525facb62ef647dddc4722456e07`
- `Linux >= b709eb872e19a19607bbb6d2975bc264d59735cf < ac7ecb65af170a7fc193e7bd8be15dac84ec6a56`
- `Linux >= b709eb872e19a19607bbb6d2975bc264d59735cf < 77de62ad3de3967818c3dbe656b7336ebee461d2`
- `Linux 6.14`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.