Linux: Use After Free
CVE-2025-21761 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 e85a25d1a9985645e796039e843d1de581d2de1e, a8816b3f1f151373fd30f1996f00480126c8bb11, a884f57600e463f69d7b279c4598b865260b62a1 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 0.26% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to e85a25d1a9985645e796039e843d1de581d2de1e or a8816b3f1f151373fd30f1996f00480126c8bb11 or a884f57600e463f69d7b279c4598b865260b62a1 or 7e01abc34e87abd091e619161a20f54ed4e3e2da, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.4.291 or 5.10.235 or 5.15.179 or 6.1.129, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 9354d452034273a50a4fd703bea31e5d6b1fc20b up to, but not including, e85a25d1a9985645e796039e843d1de581d2de1e; 9354d452034273a50a4fd703bea31e5d6b1fc20b up to, but not including, a8816b3f1f151373fd30f1996f00480126c8bb11; 9354d452034273a50a4fd703bea31e5d6b1fc20b up to, but not including, a884f57600e463f69d7b279c4598b865260b62a1; 9354d452034273a50a4fd703bea31e5d6b1fc20b up to, but not including, 7e01abc34e87abd091e619161a20f54ed4e3e2da; 9354d452034273a50a4fd703bea31e5d6b1fc20b up to, but not including, 8ec57509c36c8b9a23e50b7858dda0c520a2d074; 9354d452034273a50a4fd703bea31e5d6b1fc20b up to, but not including, a849a10de5e04d798f7f286a2f1ca174719a617a; 9354d452034273a50a4fd703bea31e5d6b1fc20b up to, but not including, 5828937742af74666192835d657095d95c53dbd0; 9354d452034273a50a4fd703bea31e5d6b1fc20b up to, but not including, 90b2f49a502fa71090d9f4fe29a2f51fe5dff76d; and 1 more ranges | e85a25d1a9985645e796039e843d1de581d2de1e, a8816b3f1f151373fd30f1996f00480126c8bb11, a884f57600e463f69d7b279c4598b865260b62a1, 7e01abc34e87abd091e619161a20f54ed4e3e2da, 8ec57509c36c8b9a23e50b7858dda0c520a2d074, a849a10de5e04d798f7f286a2f1ca174719a617a |
| Siemens | SIMATIC S7-1500 TM MFP - GNU/Linux subsystem | all versions | Not stated |
| Linux | Linux Kernel | 4.15 up to, but not including, 5.4.291; 5.5 up to, but not including, 5.10.235; 5.11 up to, but not including, 5.15.179; 5.16 up to, but not including, 6.1.129; 6.2 up to, but not including, 6.6.79; 6.7 up to, but not including, 6.12.16; 6.13 up to, but not including, 6.13.4; 6.14 | 5.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.79, 6.12.16 |
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 system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: openvswitch: use RCU protection in ovs_vport_cmd_fill_info() ovs_vport_cmd_fill_info() can be called without RTNL or RCU. Use RCU protection and dev_net_rcu() to avoid potential UAF.
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.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/5828937742af74666192835d657095d95c53dbd0
- git.kernel.org/stable/c/7e01abc34e87abd091e619161a20f54ed4e3e2da
- git.kernel.org/stable/c/8ec57509c36c8b9a23e50b7858dda0c520a2d074
- git.kernel.org/stable/c/90b2f49a502fa71090d9f4fe29a2f51fe5dff76d
- git.kernel.org/stable/c/a849a10de5e04d798f7f286a2f1ca174719a617a
- git.kernel.org/stable/c/a8816b3f1f151373fd30f1996f00480126c8bb11
- git.kernel.org/stable/c/a884f57600e463f69d7b279c4598b865260b62a1
- git.kernel.org/stable/c/e85a25d1a9985645e796039e843d1de581d2de1e
Other references
Recent Use After Free vulnerabilities
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 9.8 Critical severity
- 7.8 High severity
Spotted an error? Tell us.