Linux: Use After Free
CVE-2025-21887 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 f77618291836168eca99e89cd175256f928f5e64, 4b49d939b5a79117f939b77cc67efae2694d9799, a7c41830ffcd17b2177a95a9b99b270302090c35 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.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to f77618291836168eca99e89cd175256f928f5e64 or 4b49d939b5a79117f939b77cc67efae2694d9799 or a7c41830ffcd17b2177a95a9b99b270302090c35 or 64455c8051c3aedc71abb7ec8d47c80301f99f00, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.11 or 5.15.179 or 6.1.130 or 6.4, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 714ba10a6dd19752a349e59aa875f3288ccb59b9 up to, but not including, f77618291836168eca99e89cd175256f928f5e64; 62f29ca45f832e281fc14966ac25f6ff3bd121ca up to, but not including, 4b49d939b5a79117f939b77cc67efae2694d9799; e4f2a1feebb3f209a0fca82aa53507a5b8be4d53 up to, but not including, a7c41830ffcd17b2177a95a9b99b270302090c35; b07d5cc93e1b28df47a72c519d09d0a836043613 up to, but not including, 64455c8051c3aedc71abb7ec8d47c80301f99f00; b07d5cc93e1b28df47a72c519d09d0a836043613 up to, but not including, 3594aad97e7be2557ca9fa9c931b206b604028c8; b07d5cc93e1b28df47a72c519d09d0a836043613 up to, but not including, 60b4b5c1277fc491da9e1e7abab307bfa39c2db7; b07d5cc93e1b28df47a72c519d09d0a836043613 up to, but not including, c84e125fff2615b4d9c259e762596134eddd2f27; 33ab4dd6202f359558a0a2678b94d1b9994c17e5; and 7 more ranges | f77618291836168eca99e89cd175256f928f5e64, 4b49d939b5a79117f939b77cc67efae2694d9799, a7c41830ffcd17b2177a95a9b99b270302090c35, 64455c8051c3aedc71abb7ec8d47c80301f99f00, 3594aad97e7be2557ca9fa9c931b206b604028c8, 60b4b5c1277fc491da9e1e7abab307bfa39c2db7 |
| 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 | 5.10.188 up to, but not including, 5.11; 5.15.121 up to, but not including, 5.15.179; 6.1.39 up to, but not including, 6.1.130; 6.3.13 up to, but not including, 6.4; 6.4.4 up to, but not including, 6.6.81; 6.7 up to, but not including, 6.12.18; 6.13 up to, but not including, 6.13.6; 6.14 | 5.11, 5.15.179, 6.1.130, 6.4, 6.6.81, 6.12.18 |
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: ovl: fix UAF in ovl_dentry_update_reval by moving dput() in ovl_link_up The issue was caused by dput(upper) being called before ovl_dentry_update_reval(), while upper->d_flags was still accessed in ovl_dentry_remote(). Move dput(upper) after its last use to prevent use-after-free. BUG: KASAN: slab-use-after-free in ovl_dentry_remote fs/overlayfs/util.c:162 [inline] BUG: KASAN: slab-use-after-free in ovl_dentry_update_reval+0xd2/0xf0 fs/overlayfs/util.c:167 Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114 print_address_description mm/kasan/report.c:377 [inline] print_report+0xc3/0x620 mm/kasan/report.c:488 kasan_report+0xd9/0x110 mm/kasan/report.c:601 ovl_dentry_remote fs/overlayfs/util.c:162 [inline] ovl_dentry_update_reval+0xd2/0xf0 fs/overlayfs/util.c:167 ovl_link_up fs/overlayfs/copy_up.c:610 [inline] ovl_copy_up_one+0x2105/0x3490 fs/overlayfs/copy_up.c:1170 ovl_copy_up_flags+0x18d/0x200 fs/overlayfs/copy_up.c:1223 ovl_rename+0x39e/0x18c0 fs/overlayfs/dir.c:1136 vfs_rename+0xf84/0x20a0 fs/namei.c:4893 ... </TASK>
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/3594aad97e7be2557ca9fa9c931b206b604028c8
- git.kernel.org/stable/c/4b49d939b5a79117f939b77cc67efae2694d9799
- git.kernel.org/stable/c/60b4b5c1277fc491da9e1e7abab307bfa39c2db7
- git.kernel.org/stable/c/64455c8051c3aedc71abb7ec8d47c80301f99f00
- git.kernel.org/stable/c/a7c41830ffcd17b2177a95a9b99b270302090c35
- git.kernel.org/stable/c/c84e125fff2615b4d9c259e762596134eddd2f27
Other references
Recent Use After Free vulnerabilities
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