{"id":"CVE-2026-31680","title":"net: ipv6: flowlabel: defer exclusive option free until RCU teardown","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: flowlabel: defer exclusive option free until RCU teardown\n\n`ip6fl_seq_show()` walks the global flowlabel hash under the seq-file\nRCU read-side lock and print…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 4b6798024f7b2d535f3db1002c760143cdbd1bd3","Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827","Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 5a6b15f861b7c1304949e3350d23490a5fe429fd","Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 6c7fbdb8ffde6413640de7cfbd7c976c353e89f8","Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 8027964931785cb73d520ac70a342a3dc16c249b","Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 414726b69921fe6355ae453f5b35e68dd078342a","Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 572ce62778519a7d4d1c15f55dd2e45a474133c4","Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 9ca562bb8e66978b53028fa32b1a190708e6a091","Linux 3.9"],"published":"2026-04-25","updated":"2026-09-08","sourceUpdated":"2026-09-08T08:48:05.243Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31680","references":[{"url":"https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3"},{"url":"https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827"},{"url":"https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd"},{"url":"https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8"},{"url":"https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b"},{"url":"https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a"},{"url":"https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4"},{"url":"https://git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091"}],"tags":["cve.org"],"epss":0.00184,"epssPercentile":0.07036,"ingestedAt":"2026-09-08T15:33:26.989Z","slug":"CVE-2026-31680","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: flowlabel: defer exclusive option free until RCU teardown\n\n`ip6fl_seq_show()` walks the global flowlabel hash under the seq-file\nRCU read-side lock and prints `fl->opt->opt_nflen` when an option block\nis present.\n\nExclusive flowlabels currently free `fl->opt` as soon as `fl->users`\ndrops to zero in `fl_release()`. However, the surrounding\n`struct ip6_flowlabel` remains visible in the global hash table until\nlater garbage collection removes it and `fl_free_rcu()` finally tears it\ndown.\n\nA concurrent `/proc/net/ip6_flowlabel` reader can therefore race that\nearly `kfree()` and dereference freed option state, triggering a crash\nin `ip6fl_seq_show()`.\n\nFix this by keeping `fl->opt` alive until `fl_free_rcu()`. That matches\nthe lifetime already required for the enclosing flowlabel while readers\ncan still reach it under RCU.\n\n## Affected\n\n- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 4b6798024f7b2d535f3db1002c760143cdbd1bd3`\n- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827`\n- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 5a6b15f861b7c1304949e3350d23490a5fe429fd`\n- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 6c7fbdb8ffde6413640de7cfbd7c976c353e89f8`\n- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 8027964931785cb73d520ac70a342a3dc16c249b`\n- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 414726b69921fe6355ae453f5b35e68dd078342a`\n- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 572ce62778519a7d4d1c15f55dd2e45a474133c4`\n- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 9ca562bb8e66978b53028fa32b1a190708e6a091`\n- `Linux 3.9`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}