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CVE Record

CVE-2025-21771: sched_ext: Fix incorrect autogroup migration detection

In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix incorrect autogroup migration detection scx_move_task() is called from sched_move_task() and tells the BPF scheduler that cgroup migration is being committed. sched_move_task() is used by both cgroup and autogroup migrations and scx_move_task() tried to filter out autogroup migrations by testing the destination cgroup and PF_EXITING but this is not enough. In fact, without explicitly tagging the thread which is doing the cgroup migration, there is no good way to tell apart scx_move_task() invocations for racing migration to the root cgroup and an autogroup migration. This led to scx_move_task() incorrectly ignoring a migration from non-root cgroup to an autogroup of the root cgroup triggering the following warning: WARNING: CPU: 7 PID: 1 at kernel/sched/ext.c:3725 scx_cgroup_can_attach+0x196/0x340 ... Call Trace: <TASK> cgroup_migrate_execute+0x5b1/0x700 cgroup_attach_task+0x296/0x400 __cgroup_procs_write+0x128/0x140 cgroup_procs_write+0x17/0x30 kernfs_fop_write_iter+0x141/0x1f0 vfs_write+0x31d/0x4a0 __x64_sys_write+0x72/0xf0 do_syscall_64+0x82/0x160 entry_SYSCALL_64_after_hwframe+0x76/0x7e Fix it by adding an argument to sched_move_task() that indicates whether the moving is for a cgroup or autogroup migration. After the change, scx_move_task() is called only for cgroup migrations and renamed to scx_cgroup_move_task().

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This Linux kernel issue is a scheduler bug, not a clearly documented remote compromise. Under specific task migration conditions, the sched_ext BPF scheduler can misclassify cgroup versus autogroup movement and trigger a kernel warning. Business urgency depends on whether affected kernels and sched_ext are in use.

Executive priority

Track and patch through normal kernel maintenance unless your environment relies on sched_ext at scale. Escalate priority for high-density Linux hosts, experimental scheduler deployments, or systems showing related kernel warnings.

Technical view

scx_move_task() was called from sched_move_task() for both cgroup and autogroup migrations. Its filtering could not reliably distinguish racing root-cgroup migration from autogroup migration, causing incorrect handling and a warning in scx_cgroup_can_attach(). The fix adds an explicit migration-type argument and calls the sched_ext cgroup move path only for cgroup migrations.

Likely exposure

Exposure appears limited to Linux systems running affected kernel versions with sched_ext/BPF scheduler behavior and cgroup/autogroup task migration paths. The source bundle does not identify distributions, configurations, privileges required, or externally reachable attack surfaces.

Exploitation context

The CVE is not listed as KEV, and the provided sources do not claim active exploitation or provide exploitability details. Evidence supports a kernel correctness warning during migration handling, but not a confirmed practical attack path.

Researcher notes

The source bundle lacks CVSS, CWE, distribution impact, privilege assumptions, and exploit analysis. Treat affected-version mapping carefully and rely on vendor kernel backports, not upstream version strings alone, for remediation decisions.

Mitigation direction

  • Check vendor kernel advisories for packages containing the referenced stable fixes.
  • Prioritize hosts using affected Linux kernel versions and sched_ext features.
  • Update to a vendor-supported fixed kernel when available.
  • If no vendor fix is available, monitor kernel guidance before changing scheduler features.
  • Avoid direct wrangler-style deployment assumptions; this CVE concerns Linux kernels only.

Validation and detection

  • Inventory Linux kernel versions across servers, containers hosts, and appliances.
  • Identify systems using sched_ext or BPF scheduler functionality.
  • Compare deployed kernels against vendor advisories and referenced stable commits.
  • Review kernel logs for warnings involving scx_cgroup_can_attach or sched_ext migration.
  • Confirm remediation by verifying the installed kernel includes the vendor fix.
Prepared
Confidence
medium
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
4Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

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Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux8195136669661fdfe54e9a8923c33b31c92fc1da, 8195136669661fdfe54e9a8923c33b31c92fc1da, 8195136669661fdfe54e9a8923c33b31c92fc1daunaffected
LinuxLinux6.12, 0, 6.12.16, 6.13.4, 6.14affected
Weakness

CWE details

No CWE listed

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