Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability (CVE-2025-39682) is being actively exploited, CISA warns

Treat this as an emergency. Identify every system running Linux, apply the vendor's fix or published mitigations immediately, and check for signs of compromise. Patching alone does not remove an attacker who already got in.

CISA's required action for CVE-2025-39682: "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." US federal civilian agencies must comply by September 21, 2026.