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PatchSiren cyber security CVE debrief

CVE-2026-64136 Linux CVE debrief

A vulnerability in the Linux kernel has been resolved. The 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(). This vulnerability may impact the stability and security of Linux kernel-based systems, particularly those using SMB client functionality.

Vendor
Linux
Product
Unknown
CVSS
CRITICAL 9.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-19
Original CVE updated
2026-08-13
Advisory published
2026-07-19
Advisory updated
2026-08-13

Who should care

Linux kernel users and administrators should be aware of this vulnerability and take necessary actions to protect their systems. This includes reviewing and verifying the locking usage for tcon fields in the cifs code, monitoring system logs for potential issues related to SMB client, and applying the patch or updating to the latest Linux kernel version.

Technical summary

The vulnerability is related to the Linux kernel's SMB client implementation. A missing lock around tc_count increment inside smb2_find_smb_sess_tcon_unlocked() could lead to potential issues. The fix was introduced as part of the commit 96c4af418586 (cifs: Fix locking usage for tcon fields). This vulnerability may impact the stability and security of Linux kernel-based systems, particularly those using SMB client functionality.

Defensive priority

Medium

Recommended defensive actions

  • Apply the patch or update to the latest Linux kernel version
  • Review and verify the locking usage for tcon fields in the cifs code
  • Monitor system logs for potential issues related to SMB client
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-19T16:17:55.463Z and has not been modified since then. The NVD entry is currently Received. There is limited information available about the vulnerability, and defenders should verify the affected scope and severity with the official advisory. The vulnerability is related to the Linux kernel's SMB client implementation, and the fix was introduced as part of the commit 96c4af418586 (cifs: Fix locking usage for tcon fields).

Sources and references

Verified primary and authoritative sources

  • CVE-2026-64136 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-64136

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-64136 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-64136

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/13fb413ae22a37c69341918a6d651d19a9b0b9b7

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/4d8690dace005a38e6dbde9ecce2da3ad85c7c41

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/7df1df6f40c0720d30206aa35c0343b962350e0d

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/bf4ebdb19ff9b3cdf992b50715fe61633327416a

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/e374f4e496fef8168784f93a4477d67be34485fd

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.