Linux: Use After Free
CVE-2026-53264 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 98b2e40879abf0245be5a5b7af69e0f6ff524ac3, 18af5d2ef0c4f65787fd1280c8b23286b9f2a835, 1f1b98fea6b9ea30507d0f2fbff6750292d097e2 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 0.48% 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 98b2e40879abf0245be5a5b7af69e0f6ff524ac3 or 18af5d2ef0c4f65787fd1280c8b23286b9f2a835 or 1f1b98fea6b9ea30507d0f2fbff6750292d097e2 or 8b136f18ac4b2ace5aaad3305b3f8a5d8165a009, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.259 or 5.15.210 or 6.1.176 or 6.6.143, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da up to, but not including, 98b2e40879abf0245be5a5b7af69e0f6ff524ac3; d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da up to, but not including, 18af5d2ef0c4f65787fd1280c8b23286b9f2a835; d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da up to, but not including, 1f1b98fea6b9ea30507d0f2fbff6750292d097e2; d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da up to, but not including, 8b136f18ac4b2ace5aaad3305b3f8a5d8165a009; d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da up to, but not including, 5dd51e09020c65aa53cf128e5e3517cd53b3c113; d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da up to, but not including, b60e9391142e983fab2be53497aa8f71fdd09cd5; d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da up to, but not including, 91d105d2cbe002f9c7b43a6183adedc37e1da1f7; d7fb60b9cafb982cb2e46a267646a8dfd4f2e5da up to, but not including, 5057e1aca011e51ef51498c940ef96f3d3e8a305; and 1 more ranges | 98b2e40879abf0245be5a5b7af69e0f6ff524ac3, 18af5d2ef0c4f65787fd1280c8b23286b9f2a835, 1f1b98fea6b9ea30507d0f2fbff6750292d097e2, 8b136f18ac4b2ace5aaad3305b3f8a5d8165a009, 5dd51e09020c65aa53cf128e5e3517cd53b3c113, b60e9391142e983fab2be53497aa8f71fdd09cd5 |
| Siemens | SIMATIC S7-1500 TM MFP - GNU/Linux subsystem | all versions | Not stated |
| Linux | Linux Kernel | 4.14 up to, but not including, 5.10.259; 5.11 up to, but not including, 5.15.210; 5.16 up to, but not including, 6.1.176; 6.2 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.94; 6.13 up to, but not including, 6.18.36; 6.19 up to, but not including, 7.0.13; 7.1 | 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, 6.18.36 |
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.
Official description
In the Linux kernel, the following vulnerability has been resolved: net/sched: act_api: use RCU with deferred freeing for action lifecycle When NEWTFILTER and DELFILTER are run concurrently it is possible to create a race with an associated action. Let's illustrate with CPU0 running NEWTFILTER and CPU1 running DELFILTER: 0: mutex_lock() <-- holds the idr lock 0: rcu_read_lock() 0: p = idr_find(idr, index) <-- action p is valid (RCU protects IDR) 0: mutex_unlock() <-- releases the idr lock 1: refcount_dec_and_mutex_lock() <-- refcnt 1->0, mutex held 1: idr_remove(idr, index) <-- Action removed from IDR 1: mutex_unlock() <-- mutex released allowing us to delete the action 1: tcf_action_cleanup(p); kfree(p) <-- Kfrees p immediately, no deferral 0: refcount_inc_not_zero(&p->tcfa_refcnt) <-- ouch, UAF p points to freed memory This patch fixes the race condition between NEWTFILTER and DELFILTER by adding struct rcu_head to tc_action used in the deferral and introducing a call_rcu() in the delete path to defer the final kfree(). Note: this is a revert of commit d7fb60b9cafb ("net_sched: get rid of tcfa_rcu") but also modernization/simplification to directly use kfree_rcu(). Let's illustrate the new restored code path: 0: rcu_read_lock() 1: refcount_dec_and_mutex_lock() <-- refcnt 1->0, mutex held 1: idr_remove(idr, index) 1: mutex_unlock() 1: call_rcu(&p->tcfa_rcu, tcf_action_rcu_free) <-- defer kfree after grace period 0: p = idr_find(idr, index) 0: refcount_inc_not_zero(&p->tcfa_refcnt) <-- fails, refcnt already 0 1: rcu_read_unlock() <-- release so freeing can run after grace period After CPU1 calls idr_remove(), the object is no longer reachable through the IDR. CPU0's subsequent idr_find() will return NULL, and even if it still held a stale pointer, the immediate kfree() is now deferred until after the RCU grace period, so no UAF can occur.
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: poc, 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/18af5d2ef0c4f65787fd1280c8b23286b9f2a835
- git.kernel.org/stable/c/1f1b98fea6b9ea30507d0f2fbff6750292d097e2
- git.kernel.org/stable/c/5057e1aca011e51ef51498c940ef96f3d3e8a305
- git.kernel.org/stable/c/5dd51e09020c65aa53cf128e5e3517cd53b3c113
- git.kernel.org/stable/c/8b136f18ac4b2ace5aaad3305b3f8a5d8165a009
- git.kernel.org/stable/c/91d105d2cbe002f9c7b43a6183adedc37e1da1f7
- git.kernel.org/stable/c/98b2e40879abf0245be5a5b7af69e0f6ff524ac3
- git.kernel.org/stable/c/b60e9391142e983fab2be53497aa8f71fdd09cd5
Other references
Recent Use After Free vulnerabilities
- 7.5 High severity
- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
- 7.5 High severity
- 8.2 High severity
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