CVE-2025-39964 — Kernel
HIGHCVE-2025-39964 is a high-severity (CVSS 7.8) CWE-362 vulnerability in Kernel. It is in CISA's Known Exploited Vulnerabilities catalog (added 2026-09-18) — treat it as actively exploited and patch now. A fix is available for Kernel — see the affected versions and patch details below.
crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2026-09-18. Federal agencies were required to remediate by 2026-09-21.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2025-39964.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2025-39964 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 384,189 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
KernelReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐧Linux | Kernel | ≥ 2.6.38&&< 5.10.245 | 5.10.245 |
Affected Products
linux kernellinuxsimatic s7-1500 cpu 1518-4 pn\/dp mfp firmwaresiemenssimatic s7-1500 cpu 1518f-4 pn\/dp mfp firmwaresiemensResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Kernel to 5.10.245 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-39964 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
The AF_ALG datapath allowed two writers on the same socket, causing request payloads to interleave unpredictably and leaving the per-socket context inconsistent. The fix introduces an exclusive write ownership (ctx->write) so that only one writer can issue sendmsg() at a time, preventing state corruption.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for CVE-2025-39964 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| NVIDIA for RHEL 10 | kernel-0:6.12.0-231.20.el10nv | RHSA-2026:72059 |
| NVIDIA for RHEL 10 | kernel-0:6.12.0-259.27.el10nv | RHSA-2026:73788 |
| Red Hat Enterprise Linux 10 | kernel-0:6.12.0-211.58.1.el10_2 | RHSA-2026:70498 |
| Red Hat Enterprise Linux 10.0 Extended Update Support | kernel-0:6.12.0-55.106.1.el10_0 | RHSA-2026:71326 |
| Red Hat Enterprise Linux 7 Extended Lifecycle Support | kernel-rt-0:3.10.0-1160.164.1.rt56.1316.el7 | RHSA-2026:71657 |
| Red Hat Enterprise Linux 7 Extended Lifecycle Support | kernel-0:3.10.0-1160.164.1.el7 | RHSA-2026:71687 |
| Red Hat Enterprise Linux 8 | kernel-rt-0:4.18.0-553.166.1.rt7.507.el8_10 | RHSA-2026:70403 |
| Red Hat Enterprise Linux 8 | kernel-0:4.18.0-553.166.1.el8_10 | RHSA-2026:70402 |
Frequently Asked Questions
Is CVE-2025-39964 in your dependencies?
Find it across Linux, including transitive dependencies.