CVE-2025-39964

crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

Actively exploited (CISA KEV) High 7.8 CVSS 3.1

Description

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.

Description as published by the source, in English.

Key facts

Published: 2025-10-13
Last modified: 2026-09-19
Assigned by: Linux
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Scored by: CVE Program
Probability of exploitation: 0.3 % higher than 17 % of all known vulnerabilities
EPSS, next 30 days, model v2026.06.15
Fix available: Not registered in the sources

Actively exploited

CISA added this vulnerability to the Known Exploited Vulnerabilities catalogue on 2026-09-18, with a remediation deadline of 2026-09-21 for US federal agencies.

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.

Affected products

Vendor	Product	Versions	Status
Linux	Linux	2.6.38	Affected
Linux	Linux	≥ 0, < 2.6.38	Not affected
Linux	Linux	≥ 5.10.245, ≤ 5.10.*	Not affected
Linux	Linux	≥ 5.15.194, ≤ 5.15.*	Not affected
Linux	Linux	≥ 6.1.154, ≤ 6.1.*	Not affected
Linux	Linux	≥ 6.12.49, ≤ 6.12.*	Not affected
Linux	Linux	≥ 6.16.9, ≤ 6.16.*	Not affected
Linux	Linux	≥ 6.17, ≤ *	Not affected
Linux	Linux	≥ 6.6.108, ≤ 6.6.*	Not affected
Linux	Linux	≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce	Affected
Linux	Linux	≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < e4c1ec11132ec466f7362a95f36a506ce4dc08c9	Affected
Linux	Linux	≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8	Affected
Linux	Linux	≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 7c4491b5644e3a3708f3dbd7591be0a570135b84	Affected
Linux	Linux	≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 9aee87da5572b3a14075f501752e209801160d3d	Affected
Linux	Linux	≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 45bcf60fe49b37daab1acee57b27211ad1574042	Affected
Linux	Linux	≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285	Affected

Weakness type

CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating …

References

Does this affect you?

A vulnerability matters only if you run the product, in an affected version, somewhere an attacker can reach.

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Sources and freshness

CVE

What it is: A reference number naming one specific vulnerability, for example CVE-2024-9474.
What it tells you: Which vulnerability we are talking about, and in which product.
What it does NOT tell you: Nothing about how serious it is, whether anyone is exploiting it, or whether it concerns you.
Why it matters: Without a shared number, vendor, authority and tooling cannot discuss the same flaw.
Used with the others: The number is the key. NVD, KEV and EPSS all describe the same CVE.

NVD CWE CISA KEV EPSS

How to read this together

No single value should be used on its own. A high CVSS score does not mean a vulnerability is being exploited, and a low one does not mean it is harmless. The four sources answer four different questions.

CVE names the specific vulnerability.
NVD adds severity and technical detail about it.
CWE describes the type of mistake behind it.
CISA KEV shows that it is already being exploited.
EPSS estimates how likely exploitation is soon.

The order that decides what is urgent

Do you actually have the product?
Is the version you run affected?
Is it listed in CISA KEV?
Does it have a high EPSS score?
Is the system reachable from the internet or from others?
How important is the system to the business?
Are there compensating controls already in place?

The first two questions are not about the vulnerability at all. They are about you, and they remove most of the list before you start.

A short example

Fix this week

CVSS 6,5 (medium)

In CISA KEV: yes
EPSS: 94 per cent
A firewall facing the internet

Can be scheduled

CVSS 9,8 (critical)

In CISA KEV: no
EPSS: 0,04 per cent
A test server with no internet access

Sorted by CVSS alone, the one on the right comes first. It is the more serious flaw in theory. But the one on the left is being used against real organisations right now, and it sits where an attacker can reach it. That is the one to fix first.

The critical one still has to be fixed. It just does not have to be fixed today.

This product uses the NVD API but is not endorsed or certified by the NVD. CVE and the CVE logo are registered trademarks of The MITRE Corporation; CVE records are used under the CVE Terms of Use. CWE is a trademark of The MITRE Corporation, used per the CWE Terms of Use. KEV data from CISA (CC0). Exploitation probability from EPSS, a FIRST.org project. Open-source package data from OSV and the GitHub Advisory Database (CC-BY 4.0).

Scores and vectors are shown as published by the sources. The ordering of results is Berigo's own editorial assessment, described on the search page, and is not NVD data. An empty result never means a system is safe.