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Vulnerability record · CVE-2026-31680 · published 25 April 2026

CVE-2026-31680: Linux kernel vulnerability

Linux · Linux Kernel

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.

7.8 CVSS 3.1 High EPSS 0.18% · top 92.9%
7.8CVSS 3.1 base score
0.18%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
10References
14 Jul 2026Last modified by NVD

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.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827 Patch
https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a Patch
https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3 Patch
https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4 Patch
https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd Patch
https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8 Patch
https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b Patch
https://git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091 Patch
https://cert-portal.siemens.com/productcert/html/ssa-019113.html
https://cert-portal.siemens.com/productcert/html/ssa-082556.html

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Source: NIST National Vulnerability Database (record CVE-2026-31680), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.