Linux: Use After Free
CVE-2025-21727 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 f78170bee51469734b1a306a74fc5f777bb22ba6, f3e0b9f790f8e8065d59e67b565a83154d9f3079, 0ae2f332cfd2d74cf3ce344ec9938cf3e29c3ccd 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 f78170bee51469734b1a306a74fc5f777bb22ba6 or f3e0b9f790f8e8065d59e67b565a83154d9f3079 or 0ae2f332cfd2d74cf3ce344ec9938cf3e29c3ccd or bbccae982e9fa1d7abcb23a5ec81cb0ec883f7de, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.235 or 5.15.179 or 6.1.129 or 6.6.76, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | b128a30409356df65f1a51cff3eb986cac8cfedc up to, but not including, f78170bee51469734b1a306a74fc5f777bb22ba6; b128a30409356df65f1a51cff3eb986cac8cfedc up to, but not including, f3e0b9f790f8e8065d59e67b565a83154d9f3079; b128a30409356df65f1a51cff3eb986cac8cfedc up to, but not including, 0ae2f332cfd2d74cf3ce344ec9938cf3e29c3ccd; b128a30409356df65f1a51cff3eb986cac8cfedc up to, but not including, bbccae982e9fa1d7abcb23a5ec81cb0ec883f7de; b128a30409356df65f1a51cff3eb986cac8cfedc up to, but not including, 573ac9c70bf7885dc85d82fa44550581bfc3b738; b128a30409356df65f1a51cff3eb986cac8cfedc up to, but not including, 80231f069240d52e98b6a317456c67b2eafd0781; b128a30409356df65f1a51cff3eb986cac8cfedc up to, but not including, e01780ea4661172734118d2a5f41bc9720765668; 5.4 | f78170bee51469734b1a306a74fc5f777bb22ba6, f3e0b9f790f8e8065d59e67b565a83154d9f3079, 0ae2f332cfd2d74cf3ce344ec9938cf3e29c3ccd, bbccae982e9fa1d7abcb23a5ec81cb0ec883f7de, 573ac9c70bf7885dc85d82fa44550581bfc3b738, 80231f069240d52e98b6a317456c67b2eafd0781 |
| Siemens | SIMATIC S7-1500 TM MFP - GNU/Linux subsystem | all versions | Not stated |
| Linux | Linux Kernel | 5.4 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, 6.6.76; 6.7 up to, but not including, 6.12.13; 6.13 up to, but not including, 6.13.2 | 5.10.235, 5.15.179, 6.1.129, 6.6.76, 6.12.13, 6.13.2 |
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: padata: fix UAF in padata_reorder A bug was found when run ltp test: BUG: KASAN: slab-use-after-free in padata_find_next+0x29/0x1a0 Read of size 4 at addr ffff88bbfe003524 by task kworker/u113:2/3039206 CPU: 0 PID: 3039206 Comm: kworker/u113:2 Kdump: loaded Not tainted 6.6.0+ Workqueue: pdecrypt_parallel padata_parallel_worker Call Trace: <TASK> dump_stack_lvl+0x32/0x50 print_address_description.constprop.0+0x6b/0x3d0 print_report+0xdd/0x2c0 kasan_report+0xa5/0xd0 padata_find_next+0x29/0x1a0 padata_reorder+0x131/0x220 padata_parallel_worker+0x3d/0xc0 process_one_work+0x2ec/0x5a0 If 'mdelay(10)' is added before calling 'padata_find_next' in the 'padata_reorder' function, this issue could be reproduced easily with ltp test (pcrypt_aead01). This can be explained as bellow: pcrypt_aead_encrypt ... padata_do_parallel refcount_inc(&pd->refcnt); // add refcnt ... padata_do_serial padata_reorder // pd while (1) { padata_find_next(pd, true); // using pd queue_work_on ... padata_serial_worker crypto_del_alg padata_put_pd_cnt // sub refcnt padata_free_shell padata_put_pd(ps->pd); // pd is freed // loop again, but pd is freed // call padata_find_next, UAF } In the padata_reorder function, when it loops in 'while', if the alg is deleted, the refcnt may be decreased to 0 before entering 'padata_find_next', which leads to UAF. As mentioned in [1], do_serial is supposed to be called with BHs disabled and always happen under RCU protection, to address this issue, add synchronize_rcu() in 'padata_free_shell' wait for all _do_serial calls to finish. [1] https://lore.kernel.org/all/[email protected]/ [2] https://lore.kernel.org/linux-kernel/jfjz5d7zwbytztackem7ibzalm5lnxldi2eofeiczqmqs2m7o6@fq426cwnjtkm/
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/0ae2f332cfd2d74cf3ce344ec9938cf3e29c3ccd
- git.kernel.org/stable/c/573ac9c70bf7885dc85d82fa44550581bfc3b738
- git.kernel.org/stable/c/80231f069240d52e98b6a317456c67b2eafd0781
- git.kernel.org/stable/c/bbccae982e9fa1d7abcb23a5ec81cb0ec883f7de
- git.kernel.org/stable/c/e01780ea4661172734118d2a5f41bc9720765668
- git.kernel.org/stable/c/f3e0b9f790f8e8065d59e67b565a83154d9f3079
- git.kernel.org/stable/c/f78170bee51469734b1a306a74fc5f777bb22ba6
Other references
Recent Use After Free vulnerabilities
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