Linux: Use After Free
CVE-2026-53239 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 8fc536e9f6856230f19c7d13e71af064b6a77b22, c4c1ea36d83bf3c4569468ca5b8b614fda1bf821, 25c8c7fb3b0b9668c7d05e209f58c158d2b020c7 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 0.1% 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 8fc536e9f6856230f19c7d13e71af064b6a77b22 or c4c1ea36d83bf3c4569468ca5b8b614fda1bf821 or 25c8c7fb3b0b9668c7d05e209f58c158d2b020c7 or 42827d03f8009a6a218bacab153e21f39d6a121c, 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 | 6be3b0db6db82cf056a72cc18042048edd27f8ee up to, but not including, 8fc536e9f6856230f19c7d13e71af064b6a77b22; 6be3b0db6db82cf056a72cc18042048edd27f8ee up to, but not including, c4c1ea36d83bf3c4569468ca5b8b614fda1bf821; 6be3b0db6db82cf056a72cc18042048edd27f8ee up to, but not including, 25c8c7fb3b0b9668c7d05e209f58c158d2b020c7; 6be3b0db6db82cf056a72cc18042048edd27f8ee up to, but not including, 42827d03f8009a6a218bacab153e21f39d6a121c; 6be3b0db6db82cf056a72cc18042048edd27f8ee up to, but not including, 88697cf980222d5906a37bf47662dac0732e2a0f; 6be3b0db6db82cf056a72cc18042048edd27f8ee up to, but not including, b5316e2b8614a87d8736941972441cb47bfd4491; 6be3b0db6db82cf056a72cc18042048edd27f8ee up to, but not including, ec82ea4eb220164d854f8734ca5a35e23e577b94; 6be3b0db6db82cf056a72cc18042048edd27f8ee up to, but not including, 7f2d76c9c03257c0782afef9d95321fa04096f60; and 1 more ranges | 8fc536e9f6856230f19c7d13e71af064b6a77b22, c4c1ea36d83bf3c4569468ca5b8b614fda1bf821, 25c8c7fb3b0b9668c7d05e209f58c158d2b020c7, 42827d03f8009a6a218bacab153e21f39d6a121c, 88697cf980222d5906a37bf47662dac0732e2a0f, b5316e2b8614a87d8736941972441cb47bfd4491 |
| 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 | SIMATIC S7-1500 TM MFP - GNU/Linux subsystem | all versions | 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 | 5.0 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: xfrm: policy: fix use-after-free on inexact bin in xfrm_policy_bysel_ctx() Fix the race by pruning the bin while still holding xfrm_policy_lock, before dropping it. Use __xfrm_policy_inexact_prune_bin() directly since the lock is already held. The wrapper xfrm_policy_inexact_prune_bin() becomes unused and is removed. Race: CPU0 (XFRM_MSG_DELPOLICY) CPU1 (XFRM_MSG_NEWSPDINFO) ========================== ========================== xfrm_policy_bysel_ctx(): spin_lock_bh(xfrm_policy_lock) bin = xfrm_policy_inexact_lookup() __xfrm_policy_unlink(pol) spin_unlock_bh(xfrm_policy_lock) xfrm_policy_kill(ret) // wide window, lock not held xfrm_hash_rebuild(): spin_lock_bh(xfrm_policy_lock) __xfrm_policy_inexact_flush(): kfree_rcu(bin) // bin freed spin_unlock_bh(xfrm_policy_lock) xfrm_policy_inexact_prune_bin(bin) // UAF: bin is freed
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/25c8c7fb3b0b9668c7d05e209f58c158d2b020c7
- git.kernel.org/stable/c/42827d03f8009a6a218bacab153e21f39d6a121c
- git.kernel.org/stable/c/7f2d76c9c03257c0782afef9d95321fa04096f60
- git.kernel.org/stable/c/88697cf980222d5906a37bf47662dac0732e2a0f
- git.kernel.org/stable/c/8fc536e9f6856230f19c7d13e71af064b6a77b22
- git.kernel.org/stable/c/b5316e2b8614a87d8736941972441cb47bfd4491
- git.kernel.org/stable/c/c4c1ea36d83bf3c4569468ca5b8b614fda1bf821
- git.kernel.org/stable/c/ec82ea4eb220164d854f8734ca5a35e23e577b94
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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