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CVE-2025-39964

crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

Exploited in the wild. In CISA KEV since 2026‑09‑18. Fixed versions are out.

CVSS 3.17.8HighEPSS percentile76th1.6% chance in 30 daysCISA KEVListedsince 2026-09-18, due 2026-09-21
Public exploit: 1 sourceFix5 products4 fixed builds listed below
Check it yourself

OpenVAS · 100 checks

e.g. OID 1.3.6.1.4.1.25623.1.0.136782

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Published Updated Sources: CVE.org, NVD, BDU, CSAF

NVD CVE.org

What to do

Find your product and version, then upgrade to the build on the right.

  • LinuxAffected: ≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 0f28c4adbc4a97437874c9b669fd7958a8c6d6ceUpgrade to: 0f28c4adbc4a97437874c9b669fd7958a8c6d6ceAffected: ≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < e4c1ec11132ec466f7362a95f36a506ce4dc08c9Upgrade to: e4c1ec11132ec466f7362a95f36a506ce4dc08c9Affected: ≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8Upgrade to: 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8Affected: ≥ 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, < 7c4491b5644e3a3708f3dbd7591be0a570135b84Upgrade to: 7c4491b5644e3a3708f3dbd7591be0a570135b84 + 3 more branchesStated by: CVE record
  • Siemens Simatic S7-1500 Cpu 1518-4 Pn\/dp Mfp FirmwareAffected: 3.1.6Upgrade to: not statedStated by: NVD
  • Siemens Simatic S7-1500 Cpu 1518f-4 Pn\/dp Mfp FirmwareAffected: 3.1.6Upgrade to: not statedStated by: NVD
  • ООО «РусБИТех-Астра» Astra Linux Special EditionAffected: 1.7Upgrade to: not statedStated by: BDU
  • Сообщество свободного программного обеспечения LinuxAffected: от 2.6.38 до 5.10.245Upgrade to: not statedStated by: BDU

Versions as the sources state them. Full version matrix after sign-in

Steps

Written by AI from the record
  1. Ask IT to identify every server, workstation, appliance, and virtual machine running the Linux kernel and record its installed kernel version.
  2. Install your operating-system or device vendor’s security update containing the fix; for the 5.10 branch, update to 5.10.245 or later.
  3. Restart updated systems into the new kernel and confirm the running version after reboot.
  4. If an update is unavailable, restrict untrusted local accounts and container workloads until the vendor provides a fixed release.
Vendor advisory Usually a quick update
Check it yourselfA free OpenVAS check exists for this CVE. Run it against your hosts.Is your organisation exposed?Request an assessment to establish which checks fit your systems.

Coverage timeline

4 publishers

  1. Advisory coverage

    ·Qualys Security Blog summary

  2. Added to CISA KEV catalog

    ·CISA KEV

Sourced from public security reporting — each date is when it was published, not when it happened.

What it is

From the CVE record

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.

In plain language

Written by AI from the record

This is a serious flaw in the Linux kernel that attackers are actively using; update systems that have not received the vendor fix, including Linux kernel 5.10 systems before 5.10.245.

A locally authenticated attacker can exploit a race condition in Linux kernel AF_ALG socket handling by issuing concurrent writes, potentially compromising confidentiality, integrity, and availability.

If you're affected

  • Full system compromise
  • Business data exposure
  • Service disruption
  • Ransomware risk

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS76th
Public exploit
CISA KEV
CISA KEV

Listed as exploited in the wild since 2026-09-18.

US federal agencies must remediate by 2026-09-21.

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.
Public exploits

1 source with a proof of concept or module.

Exploit links, PoCs and Metasploit modules after sign-in
EPSS

1.6% chance of exploitation activity in the next 30 days, which ranks it in the 76th percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

The patch came 8 days before any public exploit.

  1. Patch availablerecord updated
  2. Patch availablepatch available, record updated, record updated
  3. Patch availablerecord updated
  4. Added to CISA KEVpatch available, patch available, record updated, record updated
  5. Patch availablerecord updated
  6. Patch availablerecord updated

Affected products

And 1 more affected product. See all after sign-in

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

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

Scored 7.8 by NVD.

How it is reached

  • Attack Vector LocalRequires local access to the vulnerable system (e.g. local login, malicious file)
  • Attack Complexity LowNo special conditions — the attack can be reliably reproduced
  • Privileges Required LowRequires basic user-level privileges
  • User Interaction NoneNo user interaction needed — fully automated exploitation

Scope

  • Scope UnchangedImpact is limited to the vulnerable component itself

Impact if exploited

  • Confidentiality HighTotal information disclosure — all data in the component is compromised
  • Integrity HighTotal loss of integrity — attacker can modify any data in the component
  • Availability HighTotal denial of service — the component is completely unavailable

Weaknesses

ATT&CK techniques

Mapped from the weaknesses above (CWE to ATT&CK), not observed in attacks.

Sources

References in the record

And 578 more references. See all after sign-in

In the news

Watch the software you run.

My Stack ranks new CVEs for your products by real-world exploitation, so the next exploited one reaches you without reading every advisory.

We'll flag the next CVE, public exploit or patch for Siemens, not every advisory. This one: actively exploited.