{"id":"CVE-2026-31680","state":"PUBLISHED","title":"net: ipv6: flowlabel: defer exclusive option free until RCU teardown","description":"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 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.","publishedAt":"2026-04-25T08:46:56.807Z","updatedAt":"2026-10-19T18:56:04.513Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"4b6798024f7b2d535f3db1002c760143cdbd1bd3","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"3c54b66c83fb8fcbde8e6a7bf90b65856e39f827","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"5a6b15f861b7c1304949e3350d23490a5fe429fd","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"6c7fbdb8ffde6413640de7cfbd7c976c353e89f8","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"8027964931785cb73d520ac70a342a3dc16c249b","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"414726b69921fe6355ae453f5b35e68dd078342a","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"572ce62778519a7d4d1c15f55dd2e45a474133c4","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"9ca562bb8e66978b53028fa32b1a190708e6a091","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/ip6_flowlabel.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.9","versionType":"semver"},{"version":"5.10.253","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.168","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.134","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.81","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.22","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.12","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/ip6_flowlabel.c"]}],"references":["https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3","https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827","https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd","https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8","https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b","https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a","https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4","https://git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091","https://cert-portal.siemens.com/productcert/html/ssa-082556.html","https://cert-portal.siemens.com/productcert/html/ssa-019113.html","https://cert-portal.siemens.com/productcert/html/ssa-457936.html"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31680.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31680","state":"PUBLISHED","datePublished":"2026-04-25T08:46:56.807Z","dateUpdated":"2026-10-19T18:56:04.513Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.130Z"},"containers":{"cna":{"title":"net: ipv6: flowlabel: defer exclusive option free until RCU teardown","descriptions":[{"lang":"en","value":"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 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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"4b6798024f7b2d535f3db1002c760143cdbd1bd3","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"3c54b66c83fb8fcbde8e6a7bf90b65856e39f827","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"5a6b15f861b7c1304949e3350d23490a5fe429fd","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"6c7fbdb8ffde6413640de7cfbd7c976c353e89f8","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"8027964931785cb73d520ac70a342a3dc16c249b","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"414726b69921fe6355ae453f5b35e68dd078342a","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"572ce62778519a7d4d1c15f55dd2e45a474133c4","versionType":"git"},{"version":"d3aedd5ebd4b0b925b0bcda548066803e1318499","status":"affected","lessThan":"9ca562bb8e66978b53028fa32b1a190708e6a091","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/ip6_flowlabel.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.9","versionType":"semver"},{"version":"5.10.253","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.203","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.168","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.134","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.81","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.22","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.12","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/ip6_flowlabel.c"]}],"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"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The vulnerable path is local: an attacker creates/releases IPv6 flowlabels through setsockopt(IPV6_FLOWLABEL_MGR) while reading /proc/net/ip6_flowlabel. Remote IPv6 packets do not reach this flowlabel option lifetime bug.\nAC:L - The race is between two attacker-controlled operations: flowlabel release and procfs seq-file reading. The attacker can run both sides concurrently and repeat the race without relying on external conditions.\nPR:L - Supplying the needed IPv6 option state commonly requires CAP_NET_RAW, but the check is against the socket network namespace user_ns and is reachable with low privileges via user namespaces. No real init-namespace root/admin privilege is required in the highest reasonable deployment scenario.\nUI:N - The attacker can create the socket state, release it, and read /proc/net/ip6_flowlabel directly. No victim action is required.\nS:U - This is a kernel memory lifetime bug within the same host kernel security authority. It does not cross a VM, IOMMU, or separate authorization boundary.\nC:H - The bug is a use-after-free of struct ipv6_txoptions reachable from procfs output, and freed kernel heap contents can be exposed or attacker-shaped. Per the required conservative guidance, kernel UAFs are scored High for confidentiality.\nI:H - Although the observed dereference is a stale read, this is a kernel heap use-after-free in attacker-reclaimable memory. Per the required conservative guidance and upward scoring on uncertainty, UAFs are scored High for integrity.\nA:H - A concurrent /proc/net/ip6_flowlabel reader can dereference freed option state in ip6fl_seq_show(), causing an oops or kernel crash. Kernel crashes are High availability 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