🛡️ CVE-2025-21771 — kernel

🟡 CVSS 5.5 — Medium ✅ No Known Exploit NVD
5.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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().

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

Affected software

CVE-2025-21771 is recorded against 2 packages.

  • kernel (from 6.13.0 up to 6.13.4)
  • linux-kernel

Timeline and source

Published on 27 February 2025 and last revised on 15 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
github.com (Advisory)
nvd.nist.gov (Advisory)
git.kernel.org (Package)

CVE-2025-21771 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity Medium
CVSS Score 5.5
CVSS Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE N/A
Public Exploit ✅ No
Source NVD
Published 2025-02-27
Updated 2026-08-12
Modified 2026-07-15

Affected Packages

Software From version Fixed in
kernel 6.13.0 6.13.4
linux-kernel — —

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