The Linux kernel vulnerability CVE-2026-64425 involves the io_uring/io-wq subsystem where the IO_WQ_BIT_EXIT flag was not re-checked for each linked work item during the work run loop. The initial fix only re-checked this flag at one level, allowing subsequent linked work items to reuse a stale 'do_kill = false' state, skip cancellation, and continue running after exit had started. The final fix moves the check further inside the loop to ensure all linked items are properly checked and terminated if exit is in progress. This flaw could lead to denial of service by allowing work items to run beyond intended exit points. The vulnerability affects linux-hwe-edge kernel versions prior to 7.0.0-1012.12~24.04.1 and related builds. The issue is addressed in updated kernel packages as per Ubuntu security advisories USN-8726-1 and USN-8727-1.

This vulnerability can cause denial of service conditions by allowing linked work items in the io_uring/io-wq subsystem to continue running after the kernel has initiated exit procedures. There is no impact on confidentiality or integrity reported. The CVSS score of 5.5 reflects a medium severity primarily due to impact on availability. No known exploitation in the wild has been reported.

A patch is available and should be applied by updating to the fixed kernel versions listed in the Ubuntu security advisories USN-8726-1 and USN-8727-1. After applying the update, a system reboot is required to complete remediation. Due to an ABI change, third-party kernel modules must be recompiled and reinstalled. No additional mitigation steps are indicated by the vendor.