CyberSecBulletin
CVE-2025-21726NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2025-21726 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions f4f1b1169fc3694f9bc3e28c6c68dbbf4cc744c0, 4c6209efea2208597dbd3e52dc87a0d1a8f2dbe1, 7000507bb0d2ceb545c0a690e0c707c897d102c2 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.24% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to f4f1b1169fc3694f9bc3e28c6c68dbbf4cc744c0 or 4c6209efea2208597dbd3e52dc87a0d1a8f2dbe1 or 7000507bb0d2ceb545c0a690e0c707c897d102c2 or 6f45ef616775b0ce7889b0f6077fc8d681ab30bc, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.5 or 5.10.235 or 5.15.79 or 6.1.129, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxbbefa1dd6a6d53537c11624752219e39959d04fb up to, but not including, f4f1b1169fc3694f9bc3e28c6c68dbbf4cc744c0; bbefa1dd6a6d53537c11624752219e39959d04fb up to, but not including, 4c6209efea2208597dbd3e52dc87a0d1a8f2dbe1; bbefa1dd6a6d53537c11624752219e39959d04fb up to, but not including, 7000507bb0d2ceb545c0a690e0c707c897d102c2; bbefa1dd6a6d53537c11624752219e39959d04fb up to, but not including, 6f45ef616775b0ce7889b0f6077fc8d681ab30bc; bbefa1dd6a6d53537c11624752219e39959d04fb up to, but not including, 8ca38d0ca8c3d30dd18d311f1a7ec5cb56972cac; bbefa1dd6a6d53537c11624752219e39959d04fb up to, but not including, a54091c24220a4cd847d5b4f36d678edacddbaf0; bbefa1dd6a6d53537c11624752219e39959d04fb up to, but not including, dd7d37ccf6b11f3d95e797ebe4e9e886d0332600; b4c8ed0bf977760a206997b6429a7ac91978f440; and 4 more rangesf4f1b1169fc3694f9bc3e28c6c68dbbf4cc744c0, 4c6209efea2208597dbd3e52dc87a0d1a8f2dbe1, 7000507bb0d2ceb545c0a690e0c707c897d102c2, 6f45ef616775b0ce7889b0f6077fc8d681ab30bc, 8ca38d0ca8c3d30dd18d311f1a7ec5cb56972cac, a54091c24220a4cd847d5b4f36d678edacddbaf0
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
LinuxLinux Kernel5.4.19 up to, but not including, 5.5; 5.5.3 up to, but not including, 5.10.235; 5.11 up to, but not including, 5.15.79; 5.16 up to, but not including, 6.1.129; 6.2 up to, but not including, 6.6.76; 6.7 up to, but not including, 6.12.13; 6.13 up to, but not including, 6.13.25.5, 5.10.235, 5.15.79, 6.1.129, 6.6.76, 6.12.13

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.

Scoring systemScoreSeverityScored by
CVSS 3.17.8HighCNA
CVSS 3.17.8HighCISA (ADP)

Official description

In the Linux kernel, the following vulnerability has been resolved: padata: avoid UAF for reorder_work Although the previous patch can avoid ps and ps UAF for _do_serial, it can not avoid potential UAF issue for reorder_work. This issue can happen just as below: crypto_request crypto_request crypto_del_alg padata_do_serial ... padata_reorder // processes all remaining // requests then breaks while (1) { if (!padata) break; ... } padata_do_serial // new request added list_add // sees the new request queue_work(reorder_work) padata_reorder queue_work_on(squeue->work) ... <kworker context> padata_serial_worker // completes new request, // no more outstanding // requests crypto_del_alg // free pd <kworker context> invoke_padata_reorder // UAF of pd To avoid UAF for 'reorder_work', get 'pd' ref before put 'reorder_work' into the 'serial_wq' and put 'pd' ref until the 'serial_wq' finish.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

How developers prevent this class of flaw

  • Choose a language that provides automatic memory management.
  • When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

More Use After Free vulnerabilities (CWE-416)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Use After Free vulnerabilities

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