Linux Kernel TLS Receive Path Vulnerability (CVE-2025-39682)

Catalog analysis: CISA added this entry on September 18, 2026. The entry reflects catalog information retrieved on September 19, 2026, not a snapshot archived on the inclusion date. This site’s publication date is shown separately. Check current vendor guidance before acting.

What the vulnerability is

CVE-2025-39682 is an improper check for unusual or exceptional conditions (CWE-754) located within the Linux Kernel’s TLS receive path. The flaw occurs when a zero-length record is retrieved from the rx_list, which allows it to bypass the intended recvmsg() record-type handling. This bypass can result in subsequent TLS records being processed under incorrect queuing and zero-copy assumptions.

Exposure and applicability

This vulnerability affects systems utilizing the Linux Kernel’s native TLS implementation. Because this is an open-source component, exposure extends to various distributions and proprietary implementations that incorporate the affected kernel code.

Infrastructure owners should prioritize assets with direct internet exposure and those performing high volumes of TLS-offloaded traffic. CISA has included this vulnerability in its Known Exploited Vulnerabilities (KEV) catalog as of September 18, 2026, indicating active exploitation in the wild. For covered U.S. federal agencies, a remediation deadline of September 21, 2026, has been established.

Remediation priorities

Our analysis suggests prioritizing remediation based on the asset’s role in the network perimeter and its exposure to untrusted TLS traffic.

1. Kernel Update: The primary corrective action is applying the patches provided via the kernel.org stable commits. Defenders should identify the specific commit relevant to their current kernel version.
2. Forensic Triage: Given CISA’s requirement for forensic triage, organizations should examine logs and system state for indicators of compromise before or during the patching process to ensure an attacker has not already established a foothold.
3. Lifecycle Review: Systems running end-of-life (EoL) or end-of-service (EoS) kernels that cannot be patched should be transitioned to supported versions or decommissioned, as mitigations may be unavailable for legacy versions.

How to validate remediation

To verify that exposure has been reduced, defenders must move beyond simple version checks. Validation should include:

• Commit Verification: Confirming that the specific stable kernel commits addressing CVE-2025-39682 are integrated into the running kernel image.
• Configuration Audit: Ensuring that TLS offloading or native kernel TLS features are configured in alignment with the updated kernel’s requirements.

Verification is complete when the presence of the fix is confirmed at the binary/commit level and the system has been rebooted to load the patched kernel into memory.

Limits and open questions

Applying a patch reduces the likelihood of exploitation but does not guarantee absolute prevention if other vulnerabilities exist in the network stack. There remains uncertainty regarding which specific Linux distributions have integrated these stable commits into their vendor-specific kernels. Additionally, while CISA has flagged this as exploited, the specific nature of the exploit payloads and the full range of potential impacts beyond incorrect record processing remain uncharacterized in the available source data.

Source and editorial note

CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability · Source date: September 18, 2026 · Retrieved September 19, 2026.

Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.

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