CVE-2025-39964: Linux Kernel Race Condition Vulnerability

What it is

In the Linux kernel, the following vulnerability has been resolved: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg Issuing two writes to the same af_alg socket is bogus as the data will be interleaved in an unpredictable fashion. Furthermore, concurrent writes may create inconsistencies in the internal socket state. Disallow this by adding a new ctx->write field that indiciates exclusive ownership for writing.

Exploitation evidence

First exploit evidence seen: 2026-09-18 (earliest date across the sources below).

Exploited in the wild

• CISA KEV: listed since 2026-09-18. Source

Public exploit code

GitHub proof-of-concept repositories below quality bar

2 public repositories from 2 accounts, first seen 2025-11-13.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: CISA KEV · nomi-sec/PoC-in-GitHub.

How to fix it

CISA required action

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. (source: CISA KEV)

Fixed versions

• linux linux kernel: upgrade to 5.10.245 or later (affected from 2.6.38)
• linux linux kernel: upgrade to 5.15.194 or later (affected from 5.11)
• linux linux kernel: upgrade to 6.1.154 or later (affected from 5.16)
• linux linux kernel: upgrade to 6.6.108 or later (affected from 6.2)
• linux linux kernel: upgrade to 6.12.49 or later (affected from 6.7)
• linux linux kernel: upgrade to 6.16.9 or later (affected from 6.13)

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

• https://git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce (CISA KEV notes)
• https://git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9 (CISA KEV notes)
• https://git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8 (CISA KEV notes)
• https://git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84 (CISA KEV notes)
• https://git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d (CISA KEV notes)
• https://git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042 (CISA KEV notes)
• https://git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285 (CISA KEV notes)

Detection Generic guidance

Response checklist Generic guidance

1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.