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CVE-2025-39964: Linux Kernel Race Condition Vulnerability

75
Patch now
HIGH 7.8EXPLOITEDWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2025-39964 is a high-severity flaw (CVSS 7.8) affecting linux kernel, simatic s7-1500 cpu 1518-4 pn\/dp mfp firmware, simatic s7-1500 cpu 1518f-4 pn\/dp mfp firmware, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

  • High severity
  • Exploited in the wild (CISA KEV)
  • On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score7.8 (High)
Attack vectorLocal
Attack complexityLow
Privileges neededLow
User interactionNone
EPSS exploit chance1.4% (top 28%)
CISA exploited listYes, fix due 2026-09-21
WeaknessCWE-362
Published2025-10-13
Last modified2026-10-19
Publisher (CNA): kernel.org · Vendor: linux · siemens

Am I affected?

Timeline

linux linux kernel UPGRADE
Affected: >= 2.6.38 and < 5.10.245 · >= 5.11 and < 5.15.194 · >= 5.16 and < 6.1.154 · >= 6.2 and < 6.6.108 · >= 6.7 and < 6.12.49 · >= 6.13 and < 6.16.9 · 6.17 rc1 · 6.17 rc2
Fixed in: 5.10.245, 5.15.194, 6.1.154, 6.6.108, 6.12.49, 6.16.9
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
siemens simatic s7-1500 cpu 1518-4 pn\/dp mfp firmware MITIGATE
Affected: >= 3.1.6
Fixed in: no fixed release known
Safe to downgrade to: a release before 3.1.6
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
siemens simatic s7-1500 cpu 1518f-4 pn\/dp mfp firmware MITIGATE
Affected: >= 3.1.6
Fixed in: no fixed release known
Safe to downgrade to: a release before 3.1.6
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.
Fedora 46 · retext · FIXED · 8.1.0-1.fc46 · FEDORA-2026-0602a84203 · source
sudo dnf upgrade --advisory=FEDORA-2026-0602a84203
Ubuntu 20.04 · linux · FIXED · 5.4.0-224.244
sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "5.4.0-224.244" && echo PATCHED || echo STILL-VULNERABLE
Ubuntu 22.04 · linux · FIXED · 5.15.0-164.174
sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "5.15.0-164.174" && echo PATCHED || echo STILL-VULNERABLE
Ubuntu 25.10 · linux · NOT AFFECTED
Ubuntu 24.04 · linux · FIXED · 6.8.0-90.91
sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.8.0-90.91" && echo PATCHED || echo STILL-VULNERABLE
Ubuntu 25.04 · linux · FIXED · 6.14.0-37.37
sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.14.0-37.37" && echo PATCHED || echo STILL-VULNERABLE
Debian 12 · linux · FIXED · 6.1.158-1
sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.1.158-1" && echo PATCHED || echo STILL-VULNERABLE
Debian 13 · linux · FIXED · 6.12.57-1
sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.12.57-1" && echo PATCHED || echo STILL-VULNERABLE
RHEL 10 · kernel · FIXED · kernel-6.12.0-211.58.1.el10_2
sudo dnf upgrade --advisory=RHSA-2026:70498 rpm -q kernel
RHEL 10.0 Extended Update Support · kernel · FIXED · kernel-6.12.0-55.106.1.el10_0
sudo dnf upgrade --advisory=RHSA-2026:71326 rpm -q kernel
RHEL 7 Extended Lifecycle Support · kernel-rt · FIXED · kernel-rt-3.10.0-1160.164.1.rt56.1316.el7
sudo dnf upgrade --advisory=RHSA-2026:71657 rpm -q kernel-rt
RHEL 7 Extended Lifecycle Support · kernel · FIXED · kernel-3.10.0-1160.164.1.el7
sudo dnf upgrade --advisory=RHSA-2026:71687 rpm -q kernel
RHEL 8 · kernel-rt · FIXED · kernel-rt-4.18.0-553.166.1.rt7.507.el8_10
sudo dnf upgrade --advisory=RHSA-2026:70403 rpm -q kernel-rt
Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2025-1254 · source
sudo dnf update --advisory=ALAS2023-2025-1254

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-39964?

linux kernel: upgrade to 5.10.245, 5.15.194, 6.1.154, 6.6.108, 6.12.49, 6.16.9; simatic s7-1500 cpu 1518-4 pn\/dp mfp firmware: mitigate or apply the listed mitigation; simatic s7-1500 cpu 1518f-4 pn\/dp mfp firmware: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-39964 being exploited?

Yes. CVE-2025-39964 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2025-39964 affect?

CVE-2025-39964 affects linux kernel, simatic s7-1500 cpu 1518-4 pn\/dp mfp firmware, simatic s7-1500 cpu 1518f-4 pn\/dp mfp firmware. Severity is high (CVSS 7.8). 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 fa

How urgent is CVE-2025-39964?

Priority 75/100. High severity; Exploited in the wild (CISA KEV); On your watchlist

Software pages

Linux kernel vulnerabilities

Related CVEs

References

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