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Linux KernelOperating system · Linux

CVE-2025-21771

MEDIUM · 5.5 CVSS v3.1 Published 2025-02-27
Fix available
A fix is available. Upgrade to 6.12.16 / 6.13.4 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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().

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 6.12, < 6.12.16>= 6.13, < 6.13.4= 6.14

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.12.16 / 6.13.4 or later
Fixed in 6.12.166.13.4
Vendor patch git.kernel.org →
Recommended fix High confidence

Upgrade to kernel 6.12.16 (for 6.12.x), 6.13.4 (for 6.13.x), or latest 6.14.x stable

  1. Identify the current running kernel version using `uname -r`
  2. For RHEL/CentOS systems, check if a newer kernel RPM is available: `yum check-update` or `dnf check-update`
  3. For Debian/Ubuntu systems, update package lists: `apt update` and check for new kernels: `apt-cache search linux-image`
  4. Upgrade the kernel package to version 6.12.16 or later (for 6.12.x kernels), 6.13.4 or later (for 6.13.x kernels), or the latest 6.14.x stable release
  5. For Debian/Ubuntu: `apt install linux-image-<version>` or `apt upgrade linux-image`
  6. For RHEL/CentOS: `yum update kernel` or `dnf update kernel`
  7. Reboot the system to load the fixed kernel: `systemctl reboot`
  8. Verify the new kernel version after reboot with `uname -r`
Caveat Kernel upgrades may require system reboot and could have compatibility impacts with custom modules or specific hardware drivers; test in staging first

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-21771 in production — separate from our analysis above.

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