Linux: Use After Free
CVE-2026-31680 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 4b6798024f7b2d535f3db1002c760143cdbd1bd3, 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827, 5a6b15f861b7c1304949e3350d23490a5fe429fd 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 0.16% 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 4b6798024f7b2d535f3db1002c760143cdbd1bd3 or 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827 or 5a6b15f861b7c1304949e3350d23490a5fe429fd or 6c7fbdb8ffde6413640de7cfbd7c976c353e89f8, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.10.253 or 5.15.203 or 6.1.168 or 6.6.134, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | d3aedd5ebd4b0b925b0bcda548066803e1318499 up to, but not including, 4b6798024f7b2d535f3db1002c760143cdbd1bd3; d3aedd5ebd4b0b925b0bcda548066803e1318499 up to, but not including, 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827; d3aedd5ebd4b0b925b0bcda548066803e1318499 up to, but not including, 5a6b15f861b7c1304949e3350d23490a5fe429fd; d3aedd5ebd4b0b925b0bcda548066803e1318499 up to, but not including, 6c7fbdb8ffde6413640de7cfbd7c976c353e89f8; d3aedd5ebd4b0b925b0bcda548066803e1318499 up to, but not including, 8027964931785cb73d520ac70a342a3dc16c249b; d3aedd5ebd4b0b925b0bcda548066803e1318499 up to, but not including, 414726b69921fe6355ae453f5b35e68dd078342a; d3aedd5ebd4b0b925b0bcda548066803e1318499 up to, but not including, 572ce62778519a7d4d1c15f55dd2e45a474133c4; d3aedd5ebd4b0b925b0bcda548066803e1318499 up to, but not including, 9ca562bb8e66978b53028fa32b1a190708e6a091; and 1 more ranges | 4b6798024f7b2d535f3db1002c760143cdbd1bd3, 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827, 5a6b15f861b7c1304949e3350d23490a5fe429fd, 6c7fbdb8ffde6413640de7cfbd7c976c353e89f8, 8027964931785cb73d520ac70a342a3dc16c249b, 414726b69921fe6355ae453f5b35e68dd078342a |
| 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 | 3.9 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, 6.1.168; 6.2 up to, but not including, 6.6.134; 6.7 up to, but not including, 6.12.81; 6.13 up to, but not including, 6.18.22; 6.19 up to, but not including, 6.19.12; 7.0 | 5.10.253, 5.15.203, 6.1.168, 6.6.134, 6.12.81, 6.18.22 |
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: ipv6: flowlabel: defer exclusive option free until RCU teardown `ip6fl_seq_show()` walks the global flowlabel hash under the seq-file RCU read-side lock and prints `fl->opt->opt_nflen` when an option block is present. Exclusive flowlabels currently free `fl->opt` as soon as `fl->users` drops to zero in `fl_release()`. However, the surrounding `struct ip6_flowlabel` remains visible in the global hash table until later garbage collection removes it and `fl_free_rcu()` finally tears it down. A concurrent `/proc/net/ip6_flowlabel` reader can therefore race that early `kfree()` and dereference freed option state, triggering a crash in `ip6fl_seq_show()`. Fix this by keeping `fl->opt` alive until `fl_free_rcu()`. That matches the lifetime already required for the enclosing flowlabel while readers can still reach it under RCU.
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/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827
- git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a
- git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3
- git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4
- git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd
- git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8
- git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b
- git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091
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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