Linux: Use After Free
CVE-2026-31665 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 c458fc1c278a65ad5381083121d39a479973ebed, c581e5c8f2b59158f62efe61c1a3dc36189081ff, f16fe84879a5280f05ebbcea593a189ba0f3e79a 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 0.12% 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 c458fc1c278a65ad5381083121d39a479973ebed or c581e5c8f2b59158f62efe61c1a3dc36189081ff or f16fe84879a5280f05ebbcea593a189ba0f3e79a or 070abdf1b04325b21a20a2a0c39a2208af107275, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.253 or 5.15.203 or 6.1.169 or 6.6.135, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 7e0b2b57f01d183e1c84114f1f2287737358d748 up to, but not including, c458fc1c278a65ad5381083121d39a479973ebed; 7e0b2b57f01d183e1c84114f1f2287737358d748 up to, but not including, c581e5c8f2b59158f62efe61c1a3dc36189081ff; 7e0b2b57f01d183e1c84114f1f2287737358d748 up to, but not including, f16fe84879a5280f05ebbcea593a189ba0f3e79a; 7e0b2b57f01d183e1c84114f1f2287737358d748 up to, but not including, 070abdf1b04325b21a20a2a0c39a2208af107275; 7e0b2b57f01d183e1c84114f1f2287737358d748 up to, but not including, aa7cfa16f98f8ec3e6d47c34e1a8c1ae4b9b8b77; 7e0b2b57f01d183e1c84114f1f2287737358d748 up to, but not including, b42aca3660dc2627a29a38131597ca610dc451f9; 7e0b2b57f01d183e1c84114f1f2287737358d748 up to, but not including, d0983b48c10d1509fd795c155f8b1e832e1369ff; 7e0b2b57f01d183e1c84114f1f2287737358d748 up to, but not including, f8dca15a1b190787bbd03285304b569631160eda; and 1 more ranges | c458fc1c278a65ad5381083121d39a479973ebed, c581e5c8f2b59158f62efe61c1a3dc36189081ff, f16fe84879a5280f05ebbcea593a189ba0f3e79a, 070abdf1b04325b21a20a2a0c39a2208af107275, aa7cfa16f98f8ec3e6d47c34e1a8c1ae4b9b8b77, b42aca3660dc2627a29a38131597ca610dc451f9 |
| 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 | 4.19.1 up to, but not including, 5.10.253; 5.11 up to, but not including, 5.15.203; 5.16 up to, but not including, 6.1.169; 6.2 up to, but not including, 6.6.135; 6.7 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; 4.19; and 1 more ranges | 5.10.253, 5.15.203, 6.1.169, 6.6.135, 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
- 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: netfilter: nft_ct: fix use-after-free in timeout object destroy nft_ct_timeout_obj_destroy() frees the timeout object with kfree() immediately after nf_ct_untimeout(), without waiting for an RCU grace period. Concurrent packet processing on other CPUs may still hold RCU-protected references to the timeout object obtained via rcu_dereference() in nf_ct_timeout_data(). Add an rcu_head to struct nf_ct_timeout and use kfree_rcu() to defer freeing until after an RCU grace period, matching the approach already used in nfnetlink_cttimeout.c. KASAN report: BUG: KASAN: slab-use-after-free in nf_conntrack_tcp_packet+0x1381/0x29d0 Read of size 4 at addr ffff8881035fe19c by task exploit/80 Call Trace: nf_conntrack_tcp_packet+0x1381/0x29d0 nf_conntrack_in+0x612/0x8b0 nf_hook_slow+0x70/0x100 __ip_local_out+0x1b2/0x210 tcp_sendmsg_locked+0x722/0x1580 __sys_sendto+0x2d8/0x320 Allocated by task 75: nft_ct_timeout_obj_init+0xf6/0x290 nft_obj_init+0x107/0x1b0 nf_tables_newobj+0x680/0x9c0 nfnetlink_rcv_batch+0xc29/0xe00 Freed by task 26: nft_obj_destroy+0x3f/0xa0 nf_tables_trans_destroy_work+0x51c/0x5c0 process_one_work+0x2c4/0x5a0
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/070abdf1b04325b21a20a2a0c39a2208af107275
- git.kernel.org/stable/c/aa7cfa16f98f8ec3e6d47c34e1a8c1ae4b9b8b77
- git.kernel.org/stable/c/b42aca3660dc2627a29a38131597ca610dc451f9
- git.kernel.org/stable/c/c458fc1c278a65ad5381083121d39a479973ebed
- git.kernel.org/stable/c/c581e5c8f2b59158f62efe61c1a3dc36189081ff
- git.kernel.org/stable/c/d0983b48c10d1509fd795c155f8b1e832e1369ff
- git.kernel.org/stable/c/f16fe84879a5280f05ebbcea593a189ba0f3e79a
- git.kernel.org/stable/c/f8dca15a1b190787bbd03285304b569631160eda
Other references
Recent Use After Free vulnerabilities
- 9.8 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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