Linux: Use After Free
CVE-2025-21753 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 cee55b1219568c80bf0d5dc55066e4a859baf753, c7a53757717e68af94a56929d57f1e6daff220ec, 7e954b6bb95d67ae4d1a20e9cfd83c182cf929bc 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 cee55b1219568c80bf0d5dc55066e4a859baf753 or c7a53757717e68af94a56929d57f1e6daff220ec or 7e954b6bb95d67ae4d1a20e9cfd83c182cf929bc or 6ba4663ada6c6315af23a6669d386146634808ec, 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 | 871383be592ba7e819d27556591e315a0df38cee up to, but not including, cee55b1219568c80bf0d5dc55066e4a859baf753; 871383be592ba7e819d27556591e315a0df38cee up to, but not including, c7a53757717e68af94a56929d57f1e6daff220ec; 871383be592ba7e819d27556591e315a0df38cee up to, but not including, 7e954b6bb95d67ae4d1a20e9cfd83c182cf929bc; 871383be592ba7e819d27556591e315a0df38cee up to, but not including, 6ba4663ada6c6315af23a6669d386146634808ec; 871383be592ba7e819d27556591e315a0df38cee up to, but not including, 8f5cff471039caa2b088060c074c2bf2081bcb01; 871383be592ba7e819d27556591e315a0df38cee up to, but not including, 86d71a026a7f63da905db9add845c8ee88801eca; 871383be592ba7e819d27556591e315a0df38cee up to, but not including, ce628048390dad80320d5a1f74de6ca1e1be91e7; 871383be592ba7e819d27556591e315a0df38cee up to, but not including, e2f0943cf37305dbdeaf9846e3c941451bcdef63; and 1 more ranges | cee55b1219568c80bf0d5dc55066e4a859baf753, c7a53757717e68af94a56929d57f1e6daff220ec, 7e954b6bb95d67ae4d1a20e9cfd83c182cf929bc, 6ba4663ada6c6315af23a6669d386146634808ec, 8f5cff471039caa2b088060c074c2bf2081bcb01, 86d71a026a7f63da905db9add845c8ee88801eca |
| Siemens | SIMATIC S7-1500 TM MFP - GNU/Linux subsystem | all versions | Not stated |
| Linux | Linux Kernel | 3.4 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, 6.6.78; 6.7 up to, but not including, 6.12.14; 6.13 up to, but not including, 6.13.3; 6.14 | 5.4.291, 5.10.235, 5.15.179, 6.1.129, 6.6.78, 6.12.14 |
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: btrfs: fix use-after-free when attempting to join an aborted transaction When we are trying to join the current transaction and if it's aborted, we read its 'aborted' field after unlocking fs_info->trans_lock and without holding any extra reference count on it. This means that a concurrent task that is aborting the transaction may free the transaction before we read its 'aborted' field, leading to a use-after-free. Fix this by reading the 'aborted' field while holding fs_info->trans_lock since any freeing task must first acquire that lock and set fs_info->running_transaction to NULL before freeing the transaction. This was reported by syzbot and Dmitry with the following stack traces from KASAN: ================================================================== BUG: KASAN: slab-use-after-free in join_transaction+0xd9b/0xda0 fs/btrfs/transaction.c:278 Read of size 4 at addr ffff888011839024 by task kworker/u4:9/1128 CPU: 0 UID: 0 PID: 1128 Comm: kworker/u4:9 Not tainted 6.13.0-rc7-syzkaller-00019-gc45323b7560e #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Workqueue: events_unbound btrfs_async_reclaim_data_space Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0x169/0x550 mm/kasan/report.c:489 kasan_report+0x143/0x180 mm/kasan/report.c:602 join_transaction+0xd9b/0xda0 fs/btrfs/transaction.c:278 start_transaction+0xaf8/0x1670 fs/btrfs/transaction.c:697 flush_space+0x448/0xcf0 fs/btrfs/space-info.c:803 btrfs_async_reclaim_data_space+0x159/0x510 fs/btrfs/space-info.c:1321 process_one_work kernel/workqueue.c:3236 [inline] process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317 worker_thread+0x870/0xd30 kernel/workqueue.c:3398 kthread+0x2f0/0x390 kernel/kthread.c:389 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 </TASK> Allocated by task 5315: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 poison_kmalloc_redzone mm/kasan/common.c:377 [inline] __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:394 kasan_kmalloc include/linux/kasan.h:260 [inline] __kmalloc_cache_noprof+0x243/0x390 mm/slub.c:4329 kmalloc_noprof include/linux/slab.h:901 [inline] join_transaction+0x144/0xda0 fs/btrfs/transaction.c:308 start_transaction+0xaf8/0x1670 fs/btrfs/transaction.c:697 btrfs_create_common+0x1b2/0x2e0 fs/btrfs/inode.c:6572 lookup_open fs/namei.c:3649 [inline] open_last_lookups fs/namei.c:3748 [inline] path_openat+0x1c03/0x3590 fs/namei.c:3984 do_filp_open+0x27f/0x4e0 fs/namei.c:4014 do_sys_openat2+0x13e/0x1d0 fs/open.c:1402 do_sys_open fs/open.c:1417 [inline] __do_sys_creat fs/open.c:1495 [inline] __se_sys_creat fs/open.c:1489 [inline] __x64_sys_creat+0x123/0x170 fs/open.c:1489 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task 5336: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:582 poison_slab_object mm/kasan/common.c:247 [inline] __kasan_slab_free+0x59/0x70 mm/kasan/common.c:264 kasan_slab_free include/linux/kasan.h:233 [inline] slab_free_hook mm/slub.c:2353 [inline] slab_free mm/slub.c:4613 [inline] kfree+0x196/0x430 mm/slub.c:4761 cleanup_transaction fs/btrfs/transaction.c:2063 [inline] btrfs_commit_transaction+0x2c97/0x3720 fs/btrfs/transaction.c:2598 insert_balance_item+0x1284/0x20b0 fs/btrfs/volumes.c:3757 btrfs_balance+0x992/ ---truncated---
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/6ba4663ada6c6315af23a6669d386146634808ec
- git.kernel.org/stable/c/7e954b6bb95d67ae4d1a20e9cfd83c182cf929bc
- git.kernel.org/stable/c/86d71a026a7f63da905db9add845c8ee88801eca
- git.kernel.org/stable/c/8f5cff471039caa2b088060c074c2bf2081bcb01
- git.kernel.org/stable/c/c7a53757717e68af94a56929d57f1e6daff220ec
- git.kernel.org/stable/c/ce628048390dad80320d5a1f74de6ca1e1be91e7
- git.kernel.org/stable/c/cee55b1219568c80bf0d5dc55066e4a859baf753
- git.kernel.org/stable/c/e2f0943cf37305dbdeaf9846e3c941451bcdef63
Other references
Recent Use After Free vulnerabilities
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