{"id":"CVE-2026-31504","title":"net: fix fanout UAF in packet_release() via NETDEV_UP race","summary":"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[]…","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 >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < ee642b1962caa9aa231c01abbd58bc453ae6b66e","Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 42cfd7898eeed290c9fb73f732af1f7d6b0a703e","Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 1b4c03f8892d955385c202009af7485364731bb9","Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 654386baef228c2992dbf604c819e4c7c35fc71b","Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 75fe6db23705a1d55160081f7b37db9665b1880b","Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6","Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < ceccbfc6de720ad633519a226715989cfb065af1","Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 42156f93d123436f2a27c468f18c966b7e5db796","Linux 3.1"],"published":"2026-04-22","updated":"2026-09-08","sourceUpdated":"2026-09-08T08:47:30.796Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31504","references":[{"url":"https://git.kernel.org/stable/c/ee642b1962caa9aa231c01abbd58bc453ae6b66e"},{"url":"https://git.kernel.org/stable/c/42cfd7898eeed290c9fb73f732af1f7d6b0a703e"},{"url":"https://git.kernel.org/stable/c/1b4c03f8892d955385c202009af7485364731bb9"},{"url":"https://git.kernel.org/stable/c/654386baef228c2992dbf604c819e4c7c35fc71b"},{"url":"https://git.kernel.org/stable/c/75fe6db23705a1d55160081f7b37db9665b1880b"},{"url":"https://git.kernel.org/stable/c/d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6"},{"url":"https://git.kernel.org/stable/c/ceccbfc6de720ad633519a226715989cfb065af1"},{"url":"https://git.kernel.org/stable/c/42156f93d123436f2a27c468f18c966b7e5db796"}],"tags":["cve.org"],"epss":0.00135,"epssPercentile":0.03344,"ingestedAt":"2026-09-08T15:33:26.990Z","slug":"CVE-2026-31504","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < ee642b1962caa9aa231c01abbd58bc453ae6b66e`\n- `Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 42cfd7898eeed290c9fb73f732af1f7d6b0a703e`\n- `Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 1b4c03f8892d955385c202009af7485364731bb9`\n- `Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 654386baef228c2992dbf604c819e4c7c35fc71b`\n- `Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 75fe6db23705a1d55160081f7b37db9665b1880b`\n- `Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6`\n- `Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < ceccbfc6de720ad633519a226715989cfb065af1`\n- `Linux >= ce06b03e60fc19c680d1bf873e779bf11c2fc518 < 42156f93d123436f2a27c468f18c966b7e5db796`\n- `Linux 3.1`\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":[]}