{"id":"CVE-2026-98541","title":"fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nfou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT\n\nCommit 7a9bc9e3f423 (\"fou: Don't allow 0 for FOU_ATTR_IPPROTO.\") added\nNLA_POLICY_MIN(NLA_U8, 1) to fou_nl_pol…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < fd20220f86947d66d4dba2d76f13a28dbd86ef30","Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 46b1ffb7e169c7e401dd890b29e55dbc261f8f01","Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 7f4ba56f5d310dd018972916167985010a5d66a1","Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 3bcc1624cc1cdcc05b566475d6e848093ab2a8f6","Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 8b43f40798bb2758489fbbcae7e841ad4443c213","Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < b1229b210ef5a39c58be665e6798203751411842","Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221","Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < d22609f3d13fc5baacd92c222731b03c593401db","Linux 3.18"],"published":"2026-10-18","updated":"2026-10-18","sourceUpdated":"2026-10-18T15:18:09.190Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98541","references":[{"url":"https://git.kernel.org/stable/c/fd20220f86947d66d4dba2d76f13a28dbd86ef30"},{"url":"https://git.kernel.org/stable/c/46b1ffb7e169c7e401dd890b29e55dbc261f8f01"},{"url":"https://git.kernel.org/stable/c/7f4ba56f5d310dd018972916167985010a5d66a1"},{"url":"https://git.kernel.org/stable/c/3bcc1624cc1cdcc05b566475d6e848093ab2a8f6"},{"url":"https://git.kernel.org/stable/c/8b43f40798bb2758489fbbcae7e841ad4443c213"},{"url":"https://git.kernel.org/stable/c/b1229b210ef5a39c58be665e6798203751411842"},{"url":"https://git.kernel.org/stable/c/520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221"},{"url":"https://git.kernel.org/stable/c/d22609f3d13fc5baacd92c222731b03c593401db"}],"tags":["cve.org"],"ingestedAt":"2026-10-18T15:45:12.267Z","slug":"CVE-2026-98541","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nfou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT\n\nCommit 7a9bc9e3f423 (\"fou: Don't allow 0 for FOU_ATTR_IPPROTO.\") added\nNLA_POLICY_MIN(NLA_U8, 1) to fou_nl_policy[FOU_ATTR_IPPROTO], which\nrejects an explicitly supplied FOU_ATTR_IPPROTO == 0 attribute with\n-ERANGE.\n\nHowever, FOU_ATTR_IPPROTO is an optional netlink attribute. When a user\nsends FOU_CMD_ADD with FOU_ATTR_TYPE set to FOU_ENCAP_DIRECT and omits\nFOU_ATTR_IPPROTO entirely, nla_policy validation succeeds and\nparse_nl_config() leaves cfg->protocol as 0 (from memset(cfg, 0,\nsizeof(*cfg))). fou_create() then creates a FOU_ENCAP_DIRECT socket with\nfou->protocol == 0.\n\nIn fou_udp_recv(), returning -fou->protocol to udp_queue_rcv_one_skb()\ntriggers IP protocol resubmission when fou->protocol > 0, whereas\nreturning 0 tells the UDP tunnel layer that the skb was consumed without\nfreeing it. When fou->protocol == 0, every packet received on the socket\nreturns 0 from fou_udp_recv() and leaks the sk_buff.\n\nReject FOU_ENCAP_DIRECT when !cfg->protocol in fou_create() so that\ncreating a direct encapsulation port without FOU_ATTR_IPPROTO fails with\n-EINVAL while leaving FOU_CMD_DEL and FOU_CMD_GET (which share\nparse_nl_config()) unaffected.\n\nTested in QEMU against Linux 7.3.0-rc3 by sending a FOU_CMD_ADD Generic\nNetlink request with FOU_ATTR_PORT = 5555 and FOU_ATTR_TYPE =\nFOU_ENCAP_DIRECT while omitting FOU_ATTR_IPPROTO. On the unfixed kernel,\nFOU_CMD_ADD succeeds (err = 0), FOU_CMD_GET reports fou->type = 1 and\nfou->protocol = 0, and sending 4000 UDP packets to 127.0.0.1:5555 leaks\nall 4000 sk_buffs (SUnreclaim in /proc/meminfo grows from 41456 kB to\n59008 kB, +17552 kB); with this patch applied, FOU_CMD_ADD is rejected\nwith -EINVAL (-22).\n\n## Affected\n\n- `Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < fd20220f86947d66d4dba2d76f13a28dbd86ef30`\n- `Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 46b1ffb7e169c7e401dd890b29e55dbc261f8f01`\n- `Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 7f4ba56f5d310dd018972916167985010a5d66a1`\n- `Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 3bcc1624cc1cdcc05b566475d6e848093ab2a8f6`\n- `Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 8b43f40798bb2758489fbbcae7e841ad4443c213`\n- `Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < b1229b210ef5a39c58be665e6798203751411842`\n- `Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < 520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221`\n- `Linux >= 23461551c00628c3f3fe9cf837bf53cf8f212b63 < d22609f3d13fc5baacd92c222731b03c593401db`\n- `Linux 3.18`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}