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Security Digest · Vulnerability record · Known exploited

CVE-2025-39964: Linux Kernel Race Condition Vulnerability

Exploited in the wild (CISA KEV). In the Linux kernel, the following vulnerability has been resolved: crypto: afalg - Disallow concurrent writes in afalgsendmsg Issuing two writes to the same afalg socket is bogus as the data will be interleaved in an unpredictable fashion.

CISA KEV · added 2026-09-18 CVSS 7.8 High EPSS 1.4% · p72 Patch this week

Updated By erroneo.us Security Desk14 references Seen in the digest for Sep 18, 2026

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

  • Yes, if you run Linux Kernel. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-09-18, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-09-21; treat that as the outer limit, not the target.
  • EPSS 1.4%, percentile 72: FIRST’s model estimates a 1.4% chance of exploitation activity in the next 30 days, higher than 72% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
  • Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.
  • Editorial verdict: Patch this week. Linux Kernel: Five Exploited Root Bugs Added to CISA KEV — Five local root bugs, all with fixes and most with public exploits, are now confirmed exploited; get every Linux host onto a current kernel and reboot this week, container hosts, CI runners and shared servers first.

What it is

In the Linux kernel, the following vulnerability has been resolved: crypto: afalg - Disallow concurrent writes in afalgsendmsg Issuing two writes to the same afalg 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.

CISA’s summary

Linux Kernel contains a race condition vulnerability which allows concurrent writes to the same AF_ALG socket causing data to be unpredictably interleaved and creating inconsistencies in the socket's internal state.

Weakness type: CWE-362.

Product: Linux Kernel · Assigned by: Linux · Published: 2025-10-13

Affected and fixed versions

VendorProductAffected versions (per CVE record)
LinuxLinux8ff590903d5fc7f5a0a988c38267a3d08e6393a2 < 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 < e4c1ec11132ec466f7362a95f36a506ce4dc08c9, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 < 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8, 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 <…
LinuxLinux2.6.38

Severity scores

Scored byCVSSScoreVector
Linux3.17.8 HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  • Attack vector: local access needed
  • Attack complexity: low
  • Privileges required: low (any account)
  • User interaction: none
  • Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

  • CISA KEV: added 2026-09-18; federal due date 2026-09-21. Known ransomware use: Unknown.
  • 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.
  • CISA SSVC assessment: exploitation active, automatable no, technical impact total.
  • FIRST EPSS (model of 2026-10-21): 1.36% probability of exploitation activity in the next 30 days; percentile 72.

Timeline

  • — CVE record published by Linux
  • — Added to CISA’s Known Exploited Vulnerabilities catalog
  • — erroneo.us brief: Linux Kernel: Five Exploited Root Bugs Added to CISA KEV
  • — CISA remediation deadline for US federal agencies
  • — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

  1. Listed in CISA KEV notes (git.kernel.org) git.kernel.org
  2. Listed in CISA KEV notes (git.kernel.org) git.kernel.org
  3. Listed in CISA KEV notes (git.kernel.org) git.kernel.org
  4. Listed in CISA KEV notes (git.kernel.org) git.kernel.org
  5. Listed in CISA KEV notes (git.kernel.org) git.kernel.org
  6. Listed in CISA KEV notes (git.kernel.org) git.kernel.org
  7. Listed in CISA KEV notes (git.kernel.org) git.kernel.org

Vulnerability records

  1. CVE.org record CVE-2025-39964 cve.org
  2. NVD entry CVE-2025-39964 nvd.nist.gov

Government

  1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov
  2. Listed in CISA KEV notes (cisa.gov) cisa.gov
  3. Listed in CISA KEV notes (cisa.gov) cisa.gov

Other references from the CVE record and advisory

  1. cert-portal.siemens.com cert-portal.siemens.com
  2. cert-portal.siemens.com cert-portal.siemens.com

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