High 7.8Known exploited (CISA KEV)Published Oct 13, 2025

CVE-2025-39964crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

Updated under an hour ago (Oct 27, 2026, 7:30 PM ET)

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It affects Linux and 6 other products. Add what you run to find out whether that includes you.

CISA lists it as known exploited since Sep 18, 2026; federal agencies had to remediate by Sep 21, 2026. Treat that date as your deadline.

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Exploited in the last 30 days

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.

CVSS: 7.8 HIGH (v3.1, CNA)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-362
Known exploited: Added to CISA KEV Sep 18, 2026; federal remediation due Sep 21, 2026Apply 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.
EPSS (exploitation in the next 30 days): 1.57% (percentile 75)
Assigned by: Linux
NVD analysis: Analyzed
Record last updated: Oct 14, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Linux Linux linux:linux (from the name)	8ff590903d5fc7f5a0a988c38267a3d08e6393a2 builds before 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce; from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 before e4c1ec11132ec466f7362a95f36a506ce4dc08c9; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 builds before 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 builds before 7c4491b5644e3a3708f3dbd7591be0a570135b84; from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 before 9aee87da5572b3a14075f501752e209801160d3d; from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 before 45bcf60fe49b37daab1acee57b27211ad1574042; 8ff590903d5fc7f5a0a988c38267a3d08e6393a2 builds before 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285	CNA record
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP siemens:simatic_s7_1500_cpu_1518f_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP siemens:siplus_s7_1500_cpu_1518_4_pn_dp_mfp (from the name)	from V3.1.6	CISA ADP
linux linux_kernel linux:linux_kernel	from 2.6.38 before 5.10.245; from 5.11 before 5.15.194; from 5.16 before 6.1.154; from 6.2 before 6.6.108; from 6.7 before 6.12.49; from 6.13 before 6.16.9; 6.17; 6.17; and 4 more ranges	NVD
siemens simatic_s7-1500_cpu_1518-4_pn/dp_mfp_firmware siemens:simatic_s7-1500_cpu_1518-4_pn/dp_mfp_firmware	from 3.1.6	NVD
siemens simatic_s7-1500_cpu_1518f-4_pn/dp_mfp_firmware siemens:simatic_s7-1500_cpu_1518f-4_pn/dp_mfp_firmware	from 3.1.6	NVD

References

References

https://git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce	patch
https://git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9	patch
https://git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8	patch
https://git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84	patch
https://git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d	patch
https://git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042	patch
https://git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285	patch
https://cert-portal.siemens.com/productcert/html/ssa-019113.html	third-party-advisory
https://cert-portal.siemens.com/productcert/html/ssa-457936.html	third-party-advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-39964	us-government-resource

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.