U.S. CISA adds Linux Kernel flaws to its Known Exploited Vulnerabilities catalog

Pierluigi Paganini
September 20, 2026

U.S. Cybersecurity and Infrastructure Security Agency (CISA) adds Linux Kernel flaws to its Known Exploited Vulnerabilities catalog.

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) added [1, 2] the following vulnerabilities to its Known Exploited Vulnerabilities (KEV) catalog:

CVE-2025-39682 – Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability
CVE-2025-39964 Linux Kernel Race Condition Vulnerability
CVE-2026-53266 Linux Kernel Out-of-Bounds Write Vulnerability

Below are detailed descriptions of the flaws:

CVE-2025-39682 (CVSS score: 9.8) – A flaw in the TLS receive path that fails to properly handle unexpected conditions, potentially allowing authenticated local users to expose sensitive memory contents or cause a denial-of-service (DoS).
CVE-2026-53266 (CVSS score: 8.8) – A memory corruption issue in the ebtables SNAT ARP rewrite path that could let a local attacker cause unexpected system behavior, crash the system, or gain elevated privileges.
CVE-2025-39964 (CVSS score: 7.8) – A synchronization flaw affecting AF_ALG sockets that could allow simultaneous writes to interfere with each other, potentially crashing the system or affecting the integrity of cryptographic operations.

At the time of this writing, there are currently no details on how the three vulnerabilities are being exploited in the wild, or whether they are being used together as part of a single attack chain.

According to Binding Operational Directive (BOD) 22-01: Reducing the Significant Risk of Known Exploited Vulnerabilities, FCEB agencies have to address the identified vulnerabilities by the due date to protect their networks against attacks exploiting the flaws in the catalog.

Experts also recommend that private organizations review the Catalog and address the vulnerabilities in their infrastructure.

CISA orders federal agencies to fix the above vulnerabilities by September 21, 2026.

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Pierluigi Paganini

(SecurityAffairs – hacking, CISA)

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AndyC

Andy Curtis is an award-winning security consultant, researcher and public speaker. He has been working in the computer security industry since the early 1990s, having been employed by state and federal government, leading healthcare and banking providers across three continents. He has given talks about computer security for some of the world’s largest companies, worked with law enforcement agencies on investigations into hacking groups, and is a regular voice on TV and radio explaining IT security threats.

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