CVE-2026-98463

Description

In the Linux kernel, the following vulnerability has been resolved: sched_ext: Derive SCX_RQ_IN_WAKEUP from the core enqueue flags schedule_deferred_locked() skips scheduling a deferred action while SCX_RQ_IN_WAKEUP is set and relies on the task_woken_scx() call that follows a wakeup enqueue to run it. enqueue_task_scx() sets the flag from the merged enqueue flags, which include the flags stashed for a remote activation. move_remote_task_to_local_dsq() thus sets SCX_RQ_IN_WAKEUP on the destination rq when the moved task was woken up, although no task_woken_scx() follows that activation. An IMMED insert into a busy destination requests a local reenqueue during that enqueue. The request gets linked but not scheduled and stays pending until an unrelated wakeup or preemption on that CPU runs the deferred actions. The IMMED task sits behind the running task in the meantime. If nothing runs them before the scheduler is disabled, the request outlives the scheduler and points into its freed per-cpu area, which the next scheduler dereferences from run_deferred(). Test the core enqueue flags for the wakeup bit. Only the core's wakeup path is followed by task_woken_scx().

Why is this CVE low priority?

Exploitation requires CAP_BPF in the init user namespace to load and unload sched_ext BPF schedulers via bpf(2), which on Ubuntu is only available to uid 0 (root).

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• How can I get the fixes?
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• Patch details

Patch details

References

• MITRE
• NVD
• Launchpad
• Debian

Related Ubuntu Security Notices (USN)

• USN-8959-1
• Linux kernel vulnerabilities
• 3 November 2026
• USN-8960-1
• Linux kernel (OEM) vulnerabilities
• 3 November 2026

Other references

• https://www.cve.org/CVERecord?id=CVE-2026-98463
• https://git.kernel.org/stable/c/df5cdc2c832ca4e8a6d774596b9005558761a403
• https://git.kernel.org/stable/c/3fdf2ceb31e8aff77451e468bc8409e10587916a
• https://git.kernel.org/stable/c/6c401ae426e20e53a3398a8e79afd0964c0f5110