{"id":"CVE-2026-31504","state":"PUBLISHED","title":"net: fix fanout UAF in packet_release() via NETDEV_UP race","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix fanout UAF in packet_release() via NETDEV_UP race\n\n`packet_release()` has a race window where `NETDEV_UP` can re-register a\nsocket into a fanout group's `arr[]` array. The re-registration is not\ncleaned up by `fanout_release()`, leaving a dangling pointer in the fanout\narray.\n`packet_release()` does NOT zero `po->num` in its `bind_lock` section.\nAfter releasing `bind_lock`, `po->num` is still non-zero and `po->ifindex`\nstill matches the bound device. A concurrent `packet_notifier(NETDEV_UP)`\nthat already found the socket in `sklist` can re-register the hook.\nFor fanout sockets, this re-registration calls `__fanout_link(sk, po)`\nwhich adds the socket back into `f->arr[]` and increments `f->num_members`,\nbut does NOT increment `f->sk_ref`.\n\nThe fix sets `po->num` to zero in `packet_release` while `bind_lock` is\nheld to prevent NETDEV_UP from linking, preventing the race window.\n\nThis bug was found following an additional audit with Claude Code based\non CVE-2025-38617.","publishedAt":"2026-04-22T13:54:23.862Z","updatedAt":"2026-10-19T18:45:53.946Z","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":"ce06b03e60fc19c680d1bf873e779bf11c2fc518","status":"affected","lessThan":"ee642b1962caa9aa231c01abbd58bc453ae6b66e","versionType":"git"},{"version":"ce06b03e60fc19c680d1bf873e779bf11c2fc518","status":"affected","lessThan":"42cfd7898eeed290c9fb73f732af1f7d6b0a703e","versionType":"git"},{"version":"ce06b03e60fc19c680d1bf873e779bf11c2fc518","status":"affected","lessThan":"1b4c03f8892d955385c202009af7485364731bb9","versionType":"git"},{"version":"ce06b03e60fc19c680d1bf873e779bf11c2fc518","status":"affected","lessThan":"654386baef228c2992dbf604c819e4c7c35fc71b","versionType":"git"},{"version":"ce06b03e60fc19c680d1bf873e779bf11c2fc518","status":"affected","lessThan":"75fe6db23705a1d55160081f7b37db9665b1880b","versionType":"git"},{"version":"ce06b03e60fc19c680d1bf873e779bf11c2fc518","status":"affected","lessThan":"d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6","versionType":"git"},{"version":"ce06b03e60fc19c680d1bf873e779bf11c2fc518","status":"affected","lessThan":"ceccbfc6de720ad633519a226715989cfb065af1","versionType":"git"},{"version":"ce06b03e60fc19c680d1bf873e779bf11c2fc518","status":"affected","lessThan":"42156f93d123436f2a27c468f18c966b7e5db796","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/packet/af_packet.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.1","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":"6.6.131","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.80","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.21","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.11","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/packet/af_packet.c"]}],"references":["https://git.kernel.org/stable/c/ee642b1962caa9aa231c01abbd58bc453ae6b66e","https://git.kernel.org/stable/c/42cfd7898eeed290c9fb73f732af1f7d6b0a703e","https://git.kernel.org/stable/c/1b4c03f8892d955385c202009af7485364731bb9","https://git.kernel.org/stable/c/654386baef228c2992dbf604c819e4c7c35fc71b","https://git.kernel.org/stable/c/75fe6db23705a1d55160081f7b37db9665b1880b","https://git.kernel.org/stable/c/d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6","https://git.kernel.org/stable/c/ceccbfc6de720ad633519a226715989cfb065af1","https://git.kernel.org/stable/c/42156f93d123436f2a27c468f18c966b7e5db796","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-362"],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31504.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31504","state":"PUBLISHED","datePublished":"2026-04-22T13:54:23.862Z","dateUpdated":"2026-10-19T18:45:53.946Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.105Z"},"containers":{"cna":{"title":"net: fix fanout UAF in packet_release() via NETDEV_UP race","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix fanout UAF in packet_release() via NETDEV_UP race\n\n`packet_release()` has a race window where `NETDEV_UP` can re-register a\nsocket into a fanout group's `arr[]` array. The re-registration is not\ncleaned up by `fanout_release()`, leaving a dangling pointer in the fanout\narray.\n`packet_release()` does NOT zero `po->num` in its `bind_lock` section.\nAfter releasing `bind_lock`, `po->num` is still non-zero and `po->ifindex`\nstill matches the bound device. A concurrent `packet_notifier(NETDEV_UP)`\nthat already found the socket in `sklist` can re-register the hook.\nFor fanout sockets, this re-registration calls `__fanout_link(sk, po)`\nwhich adds the socket back into `f->arr[]` and increments `f->num_members`,\nbut does NOT increment `f->sk_ref`.\n\nThe fix sets `po->num` to zero in `packet_release` while `bind_lock` is\nheld to prevent NETDEV_UP from linking, preventing the race window.\n\nThis bug was found following an additional audit with Claude Code based\non 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