{"id":"CVE-2026-31504","summary":"net: fix fanout UAF in packet_release() via NETDEV_UP race","details":"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-\u003enum` in its `bind_lock` section.\nAfter releasing `bind_lock`, `po-\u003enum` is still non-zero and `po-\u003eifindex`\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-\u003earr[]` and increments `f-\u003enum_members`,\nbut does NOT increment `f-\u003esk_ref`.\n\nThe fix sets `po-\u003enum` 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.","modified":"2026-05-18T05:59:50.025666424Z","published":"2026-04-22T13:54:23.862Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31504.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/1b4c03f8892d955385c202009af7485364731bb9"},{"type":"WEB","url":"https://git.kernel.org/stable/c/42156f93d123436f2a27c468f18c966b7e5db796"},{"type":"WEB","url":"https://git.kernel.org/stable/c/42cfd7898eeed290c9fb73f732af1f7d6b0a703e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/654386baef228c2992dbf604c819e4c7c35fc71b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/75fe6db23705a1d55160081f7b37db9665b1880b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ceccbfc6de720ad633519a226715989cfb065af1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ee642b1962caa9aa231c01abbd58bc453ae6b66e"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31504.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31504"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"ce06b03e60fc19c680d1bf873e779bf11c2fc518"},{"fixed":"ee642b1962caa9aa231c01abbd58bc453ae6b66e"},{"fixed":"42cfd7898eeed290c9fb73f732af1f7d6b0a703e"},{"fixed":"1b4c03f8892d955385c202009af7485364731bb9"},{"fixed":"654386baef228c2992dbf604c819e4c7c35fc71b"},{"fixed":"75fe6db23705a1d55160081f7b37db9665b1880b"},{"fixed":"d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6"},{"fixed":"ceccbfc6de720ad633519a226715989cfb065af1"},{"fixed":"42156f93d123436f2a27c468f18c966b7e5db796"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31504.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.1.0"},{"fixed":"5.10.253"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.203"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.168"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.131"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.80"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.21"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.11"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31504.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}