Linux Kernel's Race Condition Allows a Local Attacker to Exploit a Timing Window and Gain Elevated Privileges on the System; CISA's September 21st KEV Deadline Has Passed

Last refreshed2026-09-27

Status: KEV | Advisory ID: CVE-2025-39964

Key Details

CVE	CVE-2025-39964
Vulnerability Name	Linux Kernel Race Condition Vulnerability
CVSS Score / Version	7.8 (High) / CVSS v3.1
Updated	2026-09-20
CVSS Vector	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`
CVSS Prose	attack vector is local; attack complexity is low; privileges required is low; user interaction is none; scope is unchanged; confidentiality impact is high; integrity impact is high; availability impact is high.
Affected products	Linux Kernel, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Firmware, and Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Firmware
Exploitation status	Listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating confirmed active exploitation.
Classified as	CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition'))
KEV listing	Added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2026-09-18.
Exploitation prediction (EPSS)	1.00% probability of exploitation in the next 30 days (61% percentile) -- FIRST.org's EPSS model.
Federal remediation deadline	2026-09-21 (CISA KEV, Binding Operational Directive).

Affected Products, Subsystems & Sectors

Vendor	Product	Affected Versions	Patch Status
Linux	Kernel
Siemens	SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Firmware
Siemens	SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Firmware

Vendor

Product

Affected Versions

Patch Status

Linux

Kernel

Siemens

SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Firmware

Siemens

SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Firmware

Subsystems	Core Infrastructure, PLC/PAC/RTU
Sectors	All Sectors, Critical Manufacturing, Energy, Food and Agriculture, Transportation Systems

What to Know

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.

What to Do

Monitor Linux's and Siemens's web pages for any future patch releases.

References

Source	Reference
NVD	https://nvd.nist.gov/vuln/detail/CVE-2025-39964
CVE	https://www.cve.org/CVERecord?id=CVE-2025-39964

Source

Reference

NVD

https://nvd.nist.gov/vuln/detail/CVE-2025-39964

CVE

https://www.cve.org/CVERecord?id=CVE-2025-39964

KEV Required Action

Field	Value
KEV Link	https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Date Added to KEV	2026-09-18
Required Action Due Date	2026-09-21
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.

Field

Value

KEV Link

https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Date Added to KEV

2026-09-18

Required Action Due Date

2026-09-21

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.