Linux: Use After Free
CVE-2026-31533 is a critical-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 414fc5e5a5aff776c150f1b86770e0a25a35df3a, 02f3ecadb23558bbe068e6504118f1b712d4ece0, 0e43e0a3c94044acc74b8e0927c27972eb5a59e8 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 0.4% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Linux to 414fc5e5a5aff776c150f1b86770e0a25a35df3a or 02f3ecadb23558bbe068e6504118f1b712d4ece0 or 0e43e0a3c94044acc74b8e0927c27972eb5a59e8 or aa9facde6c5005205874c37db3fd25799d741baf, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.15.203 or 6.1.169 or 6.6.135 or 6.8, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 3ade391adc584f17b5570fd205de3ad029090368 up to, but not including, 414fc5e5a5aff776c150f1b86770e0a25a35df3a; cd1bbca03f3c1d845ce274c0d0a66de8e5929f72 up to, but not including, 02f3ecadb23558bbe068e6504118f1b712d4ece0; 13eca403876bbea3716e82cdfe6f1e6febb38754 up to, but not including, 0e43e0a3c94044acc74b8e0927c27972eb5a59e8; 8590541473188741055d27b955db0777569438e3 up to, but not including, aa9facde6c5005205874c37db3fd25799d741baf; 8590541473188741055d27b955db0777569438e3 up to, but not including, 5d70eb25b41e9b010828cd12818b06a0c3b04412; 8590541473188741055d27b955db0777569438e3 up to, but not including, 2694d408b0e595024e0fc1d64ff9db0358580f74; 8590541473188741055d27b955db0777569438e3 up to, but not including, a9b8b18364fffce4c451e6f6fd218fa4ab646705; ab6397f072e5097f267abf5cb08a8004e6b17694; and 5 more ranges | 414fc5e5a5aff776c150f1b86770e0a25a35df3a, 02f3ecadb23558bbe068e6504118f1b712d4ece0, 0e43e0a3c94044acc74b8e0927c27972eb5a59e8, aa9facde6c5005205874c37db3fd25799d741baf, 5d70eb25b41e9b010828cd12818b06a0c3b04412, 2694d408b0e595024e0fc1d64ff9db0358580f74 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.6 and later; V3.1.5 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; V3.1.5 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; V3.1.5 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; V3.1.5 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; V3.1.5 and later; V3.1.7 and later | Not stated |
| Linux | Linux Kernel | 5.15.160 up to, but not including, 5.15.203; 6.1.84 up to, but not including, 6.1.169; 6.6.18 up to, but not including, 6.6.135; 6.7.6 up to, but not including, 6.8; 6.8.1 up to, but not including, 6.12.82; 6.13 up to, but not including, 6.18.23; 6.19 up to, but not including, 6.19.13; 7.0 | 5.15.203, 6.1.169, 6.6.135, 6.8, 6.12.82, 6.18.23 |
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
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- 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:N/AC:L/PR:N/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/tls: fix use-after-free in -EBUSY error path of tls_do_encryption The -EBUSY handling in tls_do_encryption(), introduced by commit 859054147318 ("net: tls: handle backlogging of crypto requests"), has a use-after-free due to double cleanup of encrypt_pending and the scatterlist entry. When crypto_aead_encrypt() returns -EBUSY, the request is enqueued to the cryptd backlog and the async callback tls_encrypt_done() will be invoked upon completion. That callback unconditionally restores the scatterlist entry (sge->offset, sge->length) and decrements ctx->encrypt_pending. However, if tls_encrypt_async_wait() returns an error, the synchronous error path in tls_do_encryption() performs the same cleanup again, double-decrementing encrypt_pending and double-restoring the scatterlist. The double-decrement corrupts the encrypt_pending sentinel (initialized to 1), making tls_encrypt_async_wait() permanently skip the wait for pending async callbacks. A subsequent sendmsg can then free the tls_rec via bpf_exec_tx_verdict() while a cryptd callback is still pending, resulting in a use-after-free when the callback fires on the freed record. Fix this by skipping the synchronous cleanup when the -EBUSY async wait returns an error, since the callback has already handled encrypt_pending and sge restoration.
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: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/02f3ecadb23558bbe068e6504118f1b712d4ece0
- git.kernel.org/stable/c/0e43e0a3c94044acc74b8e0927c27972eb5a59e8
- git.kernel.org/stable/c/2694d408b0e595024e0fc1d64ff9db0358580f74
- git.kernel.org/stable/c/414fc5e5a5aff776c150f1b86770e0a25a35df3a
- git.kernel.org/stable/c/5d70eb25b41e9b010828cd12818b06a0c3b04412
- git.kernel.org/stable/c/a9b8b18364fffce4c451e6f6fd218fa4ab646705
- git.kernel.org/stable/c/aa9facde6c5005205874c37db3fd25799d741baf
Other references
Recent Use After Free vulnerabilities
- 9.6 Critical severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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