Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability

What it is

Linux Kernel contains an improper check for unusual or exceptional conditions vulnerability in the TLS receive path which allows a zero-length record retrieved from the rx_list to bypass the intended recvmsg() record-type handling, potentially causing subsequent TLS records to be processed using incorrect zero-copy and queuing assumptions. The impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

Who's affected

Anyone using Linux Kernel.

Under attack?

Yes. CISA added this to its catalog of actively exploited vulnerabilities on Sep 18, 2026.

What to do

Install the vendor's security update. If there isn't one yet, apply the vendor's workaround, or stop using the product until it's fixed. CISA lists this as actively exploited, so treat it as urgent.

Fixed in

See the vendor's advisory

CISA deadline

Federal agencies must fix this by Sep 21, 2026. Everyone else should treat that as a ceiling, not a target.

CISA's instruction

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.