# CVE-2025-21919

## Summary

- **CVE ID:** CVE-2025-21919
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Apr 1, 2025
- **Last Modified:** Sep 8, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

sched/fair: Fix potential memory corruption in child_cfs_rq_on_list

child_cfs_rq_on_list attempts to convert a 'prev' pointer to a cfs_rq.
This 'prev' pointer can originate from struct rq's leaf_cfs_rq_list,
making the conversion invalid and potentially leading to memory
corruption. Depending on the relative positions of leaf_cfs_rq_list and
the task group (tg) pointer within the struct, this can cause a memory
fault or access garbage data.

The issue arises in list_add_leaf_cfs_rq, where both
cfs_rq->leaf_cfs_rq_list and rq->leaf_cfs_rq_list are added to the same
leaf list. Also, rq->tmp_alone_branch can be set to rq->leaf_cfs_rq_list.

This adds a check `if (prev == &rq->leaf_cfs_rq_list)` after the main
conditional in child_cfs_rq_on_list. This ensures that the container_of
operation will convert a correct cfs_rq struct.

This check is sufficient because only cfs_rqs on the same CPU are added
to the list, so verifying the 'prev' pointer against the current rq's list
head is enough.

Fixes a potential memory corruption issue that due to current struct
layout might not be manifesting as a crash but could lead to unpredictable
behavior when the layout changes.

## Affected Products

- Linux — Linux (fdaba61ef8a268d4136d0a113d153f7a89eb9984)
- Linux — Linux (5.13)
- Linux — Linux (0)
- Linux — Linux (5.15.179)
- Linux — Linux (6.1.131)
- Linux — Linux (6.6.83)
- Linux — Linux (6.12.19)
- Linux — Linux (6.13.7)
- Linux — Linux (6.14)

## References

- [CNA](https://git.kernel.org/stable/c/5cb300dcdd27e6a351ac02541e0231261c775852)
- [CNA](https://git.kernel.org/stable/c/000c9ee43928f2ce68a156dd40bab7616256f4dd)
- [CNA](https://git.kernel.org/stable/c/9cc7f0018609f75a349e42e3aebc3b0e905ba775)
- [CNA](https://git.kernel.org/stable/c/b5741e4b9ef3567613b2351384f91d3f16e59986)
- [CNA](https://git.kernel.org/stable/c/e1dd09df30ba86716cb2ffab97dc35195c01eb8f)
- [CNA](https://git.kernel.org/stable/c/3b4035ddbfc8e4521f85569998a7569668cccf51)
- [CVE](https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html)
- [siemens-SADP](https://cert-portal.siemens.com/productcert/html/ssa-019113.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.23%
- **EPSS Percentile:** 13.8

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-19._