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CVE-2025-39964

5.5, medium Known exploited

Linux Kernel Race Condition Vulnerability

NVD (opens in a new tab) CVE.org (opens in a new tab) CISA KEV catalogue (opens in a new tab)
CVSS
5.5, medium medium CVSS v3.1
EPSS, next 30 days
1% higher than 71.2% of scored CVEs
Exploitation
Confirmed in the wild
Published
13 Oct 2025a year ago

Known exploited

CISA added this to the Known Exploited Vulnerabilities Catalog on 18 Sept 2026. US federal agencies had to remediate by 21 Sept 2026, a deadline that has passed.

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.

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.

Details

Vendor
Linux and 1 more
Product
Linux
Weakness
CWE-362 (opens in a new tab)
Status
Analyzed
Updated
15 Oct 2026
Assigner
416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

References 10

Patches and fixes 7

Advisories 2

Other references 1

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other Linux CVEs

Every Linux CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-53362 Linux Kernel Unspecified Vulnerability KEV EPSS 0.7% 7.8, high
  • CVE-2026-53266 Linux Kernel Out-of-Bounds Write Vulnerability KEV EPSS 0.8% 8.8, high
  • CVE-2026-31431 Linux Kernel Incorrect Resource Transfer Between Spheres Vulnerability KEV EPSS 3% 7.8, high
  • CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability KEV EPSS 3% 9.8, critical
  • CVE-2025-38352 Linux Kernel Time-of-Check Time-of-Use (TOCTOU) Race Condition Vulnerability KEV EPSS 1% 7.8, high
  • CVE-2024-53197 Linux Kernel Out-of-Bounds Access Vulnerability KEV EPSS 4% 7.8, high
  • CVE-2024-53150 Linux Kernel Out-of-Bounds Read Vulnerability KEV EPSS 1% 7.1, high
  • CVE-2024-53104 Linux Kernel Out-of-Bounds Write Vulnerability KEV EPSS 3% 7.8, high

Beyond this page

Is CVE-2025-39964 in your network?

This page tells you how dangerous CVE-2025-39964 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

CVE-2025-39964 is in the CISA catalogue of exploited vulnerabilities: attackers are already exploiting it.

  • EXYS7600 OCELOT

    Find it before attackers do

    Ocelot scans your network on a schedule and reports every vulnerability it finds by its CVE identifier, with its CVSS score and how many of your hosts are affected. A finding like CVE-2025-39964 comes with the devices to patch.

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  • EXYS7950 KONDRA

    Detect it if it's exploited

    Until the patch is applied, Kondra monitors your network, events and endpoints in real time. It keeps an inventory of the software installed on every endpoint, and its anomaly detection rules flag what an attacker does once inside.

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Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 17 Oct 2026, not the live upstream state.