System deadlock via non-runnable task selection
Published Apr 1, 2025 · Updated May 11, 2026
Scheduler state confusion in Linux kernel 6.12 allows local users to deadlock the system through the sched_ext scheduling path. pick_task_scx() tests whether the previous task belongs to SCX instead of verifying SCX_TASK_QUEUED, so it can select a task that is no longer runnable. Local low-privileged access and execution of the affected scheduler path are required; the resulting inconsistent task state makes potential wakers busy-loop and interrupts service.
Summary
What happened
Scheduler state confusion in Linux kernel 6.12 allows local users to deadlock the system through the sched_ext scheduling path. pick_task_scx() tests whether the previous task belongs to SCX instead of verifying SCX_TASK_QUEUED, so it can select a task that is no longer runnable. Local low-privileged access and execution of the affected scheduler path are required; the resulting inconsistent task state makes potential wakers busy-loop and interrupts service.
The record
- CVE
- CVE-2025-21897
- Published
- Apr 1, 2025
- Updated
- May 11, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux
- Classifications
- T1499.004
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 1, 2025CVE publishedPublication date reported by the CVE source.
- May 11, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=6.12
- Affected versionversion=a6250aa251eacaf3ebfcfe152a96a727fd483ecd <5324c459f90d16b0c43a78b494c598915d782b7a
- Affected versionversion=a6250aa251eacaf3ebfcfe152a96a727fd483ecd <8fef0a3b17bb258130a4fcbcb5addf94b25e9ec5
- Affected versionversion=a6250aa251eacaf3ebfcfe152a96a727fd483ecd <de60a31cb0bcacfaf9487546eac5e70e0a9c66d7
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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