CISA Adds Three Actively Exploited Linux Kernel Vulnerabilities to KEV Catalog

The U.S. Cybersecurity and Infrastructure Security Agency has added three vulnerabilities affecting the Linux Kernel to its Known Exploited Vulnerabilities catalog. The flaws, identified as CVE-2025-39682, CVE-2026-53266, and CVE-2025-39964, are confirmed to be under active exploitation in the wild. CISA is directing all federal agencies to apply patches immediately and to search for indicators of compromise. The vulnerabilities impact the kernel's kTLS TLS processing, the ebtables network bridge component, and the AF_ALG cryptographic interface. Each issue can lead to memory corruption or inconsistent internal state that attackers may leverage for privilege escalation or remote code execution.

Security NEXTSeptember 19, 2026Translated from Japanese

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The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has added three vulnerabilities in the Linux Kernel to its Known Exploited Vulnerabilities (KEV) catalog, confirming that the flaws are being actively exploited.

On 18 September 2026, CISA updated the catalog with CVE-2025-39682, CVE-2026-53266, and CVE-2025-39964. Federal civilian agencies are required to remediate the issues within the mandated timeframe and to investigate systems for signs of compromise.

CVE-2025-39682 – kTLS Zero-Length Record Handling

The first vulnerability resides in the kernel TLS implementation known as kTLS. A specially crafted TLS record with zero length is not processed correctly, allowing subsequent records to be interpreted under incorrect assumptions. This flaw can be triggered over the network and may result in memory corruption.

CVE-2026-53266 – ebtables Out-of-Bounds Write

The second issue affects the ebtables packet-filtering framework used for network bridging. When rewriting the source MAC address of ARP packets, an out-of-bounds write occurs, potentially allowing an attacker to corrupt kernel memory and escalate privileges.

CVE-2025-39964 – AF_ALG Race Condition

The third vulnerability is located in the AF_ALG interface that exposes cryptographic algorithms to user space. A race condition arises when multiple concurrent writes are performed on the same socket, leading to data mixing and inconsistent internal socket state that can be abused by local attackers.

CISA continues to urge organizations to apply available patches and monitor for exploitation attempts against these Linux Kernel components.

CISA Linux kernel CVE-2025-39682 CVE-2026-53266 CVE-2025-39964 kTLS ebtables

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