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

Technical Analysis

The vulnerability resides in the kernel's TLS (kTLS) socket layer, specifically in how recvmsg() processes records retrieved from the internal rx_list queue. When a zero-length record is present, the improper exceptional-condition check allows it to slip past record-type validation, causing the kernel to misapply zero-copy and queuing logic to subsequent TLS records. This can result in memory corruption, information disclosure, or denial of service, and given kernel-level exploitation, may enable privilege escalation or data leakage from adjacent processes. CISA KEV listing confirms this is being actively exploited, and affected builds may be EoL/EoS with no vendor patch forthcoming, requiring compensating controls. Any Linux host running kTLS-enabled workloads—including reverse proxies, API gateways, and TLS-terminating middleware commonly used in front of AI agent inference endpoints, RAG vector databases, or LLM orchestration services—could be impacted, potentially exposing API keys, session tokens, or model inference traffic transiting through affected TLS sockets. Organizations running agent frameworks on containerized or bare-metal Linux infrastructure using kTLS acceleration (e.g., for high-throughput API traffic) should treat this as a priority patch/mitigation item.

Affected Systems

Linux Kernel versions implementing kernel TLS (kTLS) socket offload in the TLS receive path; specific EoL/EoS kernel versions and distributions as identified by CISA KEV entry (exact version ranges pending vendor advisory confirmation)

Indicators of Compromise

• No specific file hashes, IPs, or domains published for this kernel-level vulnerability; exploitation is likely local/network-based against kTLS socket handling rather than via identifiable network artifacts

Remediation Steps

1. 1

   Apply Kernel Patch

   Update to a patched Linux kernel version that corrects the TLS rx_list zero-length record handling as soon as vendor patches are available.

2. 2

   Migrate from EoL Systems

   Identify and migrate any Linux systems running end-of-life or end-of-service kernel versions to currently supported releases, since no security fix will be issued for EoL branches.

3. 3

   Disable kTLS Where Not Required

   For systems where kernel TLS offload is not essential, disable kTLS and use userspace TLS termination as a temporary mitigation.

4. 4

   Monitor for Exploitation

   Review CISA KEV guidance and apply the mandated remediation timeline; monitor kernel logs and network stack behavior for anomalies consistent with TLS record processing errors.

5. 5

   Audit Agent Infrastructure

   Inventory AI agent, LLM gateway, and RAG pipeline hosts for kTLS usage and prioritize patching or isolation of any nodes handling sensitive API keys or inference traffic over affected TLS paths.