Linux: Use After Free
CVE-2025-39826 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.0 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 fb07156cc0742ba4e93dfcc84280c011d05b301f, f8c29fc437d03a98fb075c31c5be761cc8326284, 0085b250fcc79f900c82a69980ec2f3e1871823b 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 0.21% 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 fb07156cc0742ba4e93dfcc84280c011d05b301f or f8c29fc437d03a98fb075c31c5be761cc8326284 or 0085b250fcc79f900c82a69980ec2f3e1871823b or 203e4f42596ede31498744018716a3db6dbb7f51, whichever matches your release line, or a later version.
- Update SIMATIC CN 4100 to V5.0 or a later version.
- Update Linux Kernel to 6.1.150 or 6.6.104 or 6.12.45 or 6.16.5, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, fb07156cc0742ba4e93dfcc84280c011d05b301f; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, f8c29fc437d03a98fb075c31c5be761cc8326284; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 0085b250fcc79f900c82a69980ec2f3e1871823b; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, 203e4f42596ede31498744018716a3db6dbb7f51; 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 up to, but not including, d860d1faa6b2ce3becfdb8b0c2b048ad31800061; 2.6.12 | fb07156cc0742ba4e93dfcc84280c011d05b301f, f8c29fc437d03a98fb075c31c5be761cc8326284, 0085b250fcc79f900c82a69980ec2f3e1871823b, 203e4f42596ede31498744018716a3db6dbb7f51, d860d1faa6b2ce3becfdb8b0c2b048ad31800061 |
| Siemens | SIMATIC CN 4100 | before V5.0 | V5.0 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | V3.1.6 and later; V3.1.7 and later | Not stated |
| Linux | Linux Kernel | 2.6.12.1 up to, but not including, 6.1.150; 6.2 up to, but not including, 6.6.104; 6.7 up to, but not including, 6.12.45; 6.13 up to, but not including, 6.16.5; 2.6.12; 6.17 | 6.1.150, 6.6.104, 6.12.45, 6.16.5 |
| Debian | Debian Linux | 11.0 | Not 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
- HighSuccess depends on conditions outside the attacker's control.
- 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:H/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.8 | High | CNA |
| CVSS 3.1 | 7.0 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: net: rose: convert 'use' field to refcount_t The 'use' field in struct rose_neigh is used as a reference counter but lacks atomicity. This can lead to race conditions where a rose_neigh structure is freed while still being referenced by other code paths. For example, when rose_neigh->use becomes zero during an ioctl operation via rose_rt_ioctl(), the structure may be removed while its timer is still active, potentially causing use-after-free issues. This patch changes the type of 'use' from unsigned short to refcount_t and updates all code paths to use rose_neigh_hold() and rose_neigh_put() which operate reference counts atomically.
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.
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/0085b250fcc79f900c82a69980ec2f3e1871823b
- git.kernel.org/stable/c/203e4f42596ede31498744018716a3db6dbb7f51
- git.kernel.org/stable/c/d860d1faa6b2ce3becfdb8b0c2b048ad31800061
- git.kernel.org/stable/c/f8c29fc437d03a98fb075c31c5be761cc8326284
- git.kernel.org/stable/c/fb07156cc0742ba4e93dfcc84280c011d05b301f
Third-party and government advisories
- lists.debian.org/debian-lts-announce/2025/10/msg00008.htmlMailing List, Third Party Advisory
Other references
Recent Use After Free vulnerabilities
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- 7.8 High severity
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