{"id":"CVE-2026-98541","state":"PUBLISHED","title":"fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT","description":"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_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).","publishedAt":"2026-10-18T15:18:09.190Z","updatedAt":"2026-10-19T09:21:24.620Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"fd20220f86947d66d4dba2d76f13a28dbd86ef30","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"46b1ffb7e169c7e401dd890b29e55dbc261f8f01","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"7f4ba56f5d310dd018972916167985010a5d66a1","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"3bcc1624cc1cdcc05b566475d6e848093ab2a8f6","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"8b43f40798bb2758489fbbcae7e841ad4443c213","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"b1229b210ef5a39c58be665e6798203751411842","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"d22609f3d13fc5baacd92c222731b03c593401db","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fou_core.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.18","versionType":"semver"},{"version":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.112","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.55","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.9","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fou_core.c"]}],"references":["https://git.kernel.org/stable/c/fd20220f86947d66d4dba2d76f13a28dbd86ef30","https://git.kernel.org/stable/c/46b1ffb7e169c7e401dd890b29e55dbc261f8f01","https://git.kernel.org/stable/c/7f4ba56f5d310dd018972916167985010a5d66a1","https://git.kernel.org/stable/c/3bcc1624cc1cdcc05b566475d6e848093ab2a8f6","https://git.kernel.org/stable/c/8b43f40798bb2758489fbbcae7e841ad4443c213","https://git.kernel.org/stable/c/b1229b210ef5a39c58be665e6798203751411842","https://git.kernel.org/stable/c/520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221","https://git.kernel.org/stable/c/d22609f3d13fc5baacd92c222731b03c593401db"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98541.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98541","state":"PUBLISHED","datePublished":"2026-10-18T15:18:09.190Z","dateUpdated":"2026-10-19T09:21:24.620Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.356Z"},"containers":{"cna":{"title":"fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT","descriptions":[{"lang":"en","value":"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_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)."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"fd20220f86947d66d4dba2d76f13a28dbd86ef30","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"46b1ffb7e169c7e401dd890b29e55dbc261f8f01","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"7f4ba56f5d310dd018972916167985010a5d66a1","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"3bcc1624cc1cdcc05b566475d6e848093ab2a8f6","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"8b43f40798bb2758489fbbcae7e841ad4443c213","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"b1229b210ef5a39c58be665e6798203751411842","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221","versionType":"git"},{"version":"23461551c00628c3f3fe9cf837bf53cf8f212b63","status":"affected","lessThan":"d22609f3d13fc5baacd92c222731b03c593401db","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fou_core.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.18","versionType":"semver"},{"version":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.112","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.55","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.9","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fou_core.c"]}],"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"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T09:21:24.620Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"5.10.271"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"5.15.222"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.1.189"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.6.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.12.112"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.18.55"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"7.2.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}