CyberSecBulletin
CVE-2025-37797NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2025-37797 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 28b09a067831f7317c3841812276022d6c940677, 39b9095dd3b55d9b2743df038c32138efa34a9de, fcc8ede663569c704fb00a702973bd6c00373283 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 0.22% 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 28b09a067831f7317c3841812276022d6c940677 or 39b9095dd3b55d9b2743df038c32138efa34a9de or fcc8ede663569c704fb00a702973bd6c00373283 or 20d584a33e480ae80d105f43e0e7b56784da41b9, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.4.293 or 5.10.237 or 5.15.181 or 6.1.136, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14 up to, but not including, 28b09a067831f7317c3841812276022d6c940677; 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14 up to, but not including, 39b9095dd3b55d9b2743df038c32138efa34a9de; 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14 up to, but not including, fcc8ede663569c704fb00a702973bd6c00373283; 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14 up to, but not including, 20d584a33e480ae80d105f43e0e7b56784da41b9; 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14 up to, but not including, 3aa852e3605000d5c47035c3fc3a986d14ccfa9f; 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14 up to, but not including, 86cd4641c713455a4f1c8e54c370c598c2b1cee0; 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14 up to, but not including, bb583c88d23b72d8d16453d24856c99bd93dadf5; 21f4d5cc25ec0e6e8eb8420dd2c399e6d2fc7d14 up to, but not including, 3df275ef0a6ae181e8428a6589ef5d5231e58b5c; and 1 more ranges28b09a067831f7317c3841812276022d6c940677, 39b9095dd3b55d9b2743df038c32138efa34a9de, fcc8ede663569c704fb00a702973bd6c00373283, 20d584a33e480ae80d105f43e0e7b56784da41b9, 3aa852e3605000d5c47035c3fc3a986d14ccfa9f, 86cd4641c713455a4f1c8e54c370c598c2b1cee0
LinuxLinux Kernel4.14.1 up to, but not including, 5.4.293; 5.5 up to, but not including, 5.10.237; 5.11 up to, but not including, 5.15.181; 5.16 up to, but not including, 6.1.136; 6.2 up to, but not including, 6.6.89; 6.7 up to, but not including, 6.12.26; 6.13 up to, but not including, 6.14.5; 4.14; and 1 more ranges5.4.293, 5.10.237, 5.15.181, 6.1.136, 6.6.89, 6.12.26
DebianDebian Linux11.0Not stated

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 NVD.

Scoring systemScoreSeverityScored by
CVSS 3.17.8HighCNA
CVSS 3.17.8HighNVD

Official description

In the Linux kernel, the following vulnerability has been resolved: net_sched: hfsc: Fix a UAF vulnerability in class handling This patch fixes a Use-After-Free vulnerability in the HFSC qdisc class handling. The issue occurs due to a time-of-check/time-of-use condition in hfsc_change_class() when working with certain child qdiscs like netem or codel. The vulnerability works as follows: 1. hfsc_change_class() checks if a class has packets (q.qlen != 0) 2. It then calls qdisc_peek_len(), which for certain qdiscs (e.g., codel, netem) might drop packets and empty the queue 3. The code continues assuming the queue is still non-empty, adding the class to vttree 4. This breaks HFSC scheduler assumptions that only non-empty classes are in vttree 5. Later, when the class is destroyed, this can lead to a Use-After-Free The fix adds a second queue length check after qdisc_peek_len() to verify the queue wasn't emptied.

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

Third-party and government advisories

Recent Use After Free vulnerabilities

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