{"id":"CVE-2026-97984","state":"PUBLISHED","title":"net: ipv6: Fix UDP length overflow with PMTU discover and big MTU","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: Fix UDP length overflow with PMTU discover and big MTU\n\nThis commit bounds cork->base.fragsize to IP6_MAX_MTU for UDP sockets to\navoid a possible overflow of UDP length that triggers a WARN in\nudp_set_len_short when setsockopt IPV6_MTU_DISCOVER is set to\nIPV6_PMTUDISC_DO or IPV6_PMTUDISC_PROBE, and a large packet is sent over\na netdev with an unusually large MTU.\n\nSteps to reproduce (included in the new selftest):\n\n1. Set device MTU bigger than IP6_MAX_MTU. cork->base.fragsize will be\n   set to that MTU in ip6_setup_cork.\n2. Set IPV6_MTU_DISCOVER to IPV6_PMTUDISC_PROBE or IPV6_PMTUDISC_DO. It\n   lets maxnonfragsize be set to device MTU (cork->fragsize) in\n   __ip6_append_data, rather than to IP6_MAX_MTU.\n3. Send 65528 bytes of payload (+8 bytes of UDP header, +40 bytes of\n   IPv6 header). Device MTU allows it (it's only one byte bigger than\n   IP6_MAX_MTU, and the device MTU is bigger than that).\n4. The UDP length in the built packet is 65536, which overflows the\n   16-bit length field and triggers the WARN in udp_set_len_short.\n\nTo avoid breaking sending UDP jumbograms over raw IPv6 sockets, limit\nthe change to UDP sockets only.\n\nThe original overflow bug with IPv6 and IPV6_PMTUDISC_DO seems to\npredate git history (verified reproduction on 2.6.21), was fixed later,\nand then reappeared in commit 427faee167bc (\"net: ipv6: introduce\nip6_dst_mtu_maybe_forward\"), which is chosen as the Fixes tag here. The\noverflow with IPV6_PMTUDISC_PROBE reproduces since its introduction in\ncommit 628a5c561890 (\"[INET]: Add IP(V6)_PMTUDISC_RPOBE\").","publishedAt":"2026-09-25T10:23:19.568Z","updatedAt":"2026-10-19T09:11:51.310Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"1dd562f3019019ffdf4b396570613053facda9ee","versionType":"git"},{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"1d56a00ec91f2885c64ea5b8cea18cb746b91bbb","versionType":"git"},{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"ce66352d3eb21825410af8b91db7cc4bb8e22c98","versionType":"git"},{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc","versionType":"git"},{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"0ae10b6be49b425827659b23bcce498f80eb7182","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/ip6_output.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.15","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","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/ipv6/ip6_output.c"]}],"references":["https://git.kernel.org/stable/c/1dd562f3019019ffdf4b396570613053facda9ee","https://git.kernel.org/stable/c/1d56a00ec91f2885c64ea5b8cea18cb746b91bbb","https://git.kernel.org/stable/c/ce66352d3eb21825410af8b91db7cc4bb8e22c98","https://git.kernel.org/stable/c/e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc","https://git.kernel.org/stable/c/0ae10b6be49b425827659b23bcce498f80eb7182"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/97xxx/CVE-2026-97984.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-97984","state":"PUBLISHED","datePublished":"2026-09-25T10:23:19.568Z","dateUpdated":"2026-10-19T09:11:51.310Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:18:58.208Z"},"containers":{"cna":{"title":"net: ipv6: Fix UDP length overflow with PMTU discover and big MTU","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: Fix UDP length overflow with PMTU discover and big MTU\n\nThis commit bounds cork->base.fragsize to IP6_MAX_MTU for UDP sockets to\navoid a possible overflow of UDP length that triggers a WARN in\nudp_set_len_short when setsockopt IPV6_MTU_DISCOVER is set to\nIPV6_PMTUDISC_DO or IPV6_PMTUDISC_PROBE, and a large packet is sent over\na netdev with an unusually large MTU.\n\nSteps to reproduce (included in the new selftest):\n\n1. Set device MTU bigger than IP6_MAX_MTU. cork->base.fragsize will be\n   set to that MTU in ip6_setup_cork.\n2. Set IPV6_MTU_DISCOVER to IPV6_PMTUDISC_PROBE or IPV6_PMTUDISC_DO. It\n   lets maxnonfragsize be set to device MTU (cork->fragsize) in\n   __ip6_append_data, rather than to IP6_MAX_MTU.\n3. Send 65528 bytes of payload (+8 bytes of UDP header, +40 bytes of\n   IPv6 header). Device MTU allows it (it's only one byte bigger than\n   IP6_MAX_MTU, and the device MTU is bigger than that).\n4. The UDP length in the built packet is 65536, which overflows the\n   16-bit length field and triggers the WARN in udp_set_len_short.\n\nTo avoid breaking sending UDP jumbograms over raw IPv6 sockets, limit\nthe change to UDP sockets only.\n\nThe original overflow bug with IPv6 and IPV6_PMTUDISC_DO seems to\npredate git history (verified reproduction on 2.6.21), was fixed later,\nand then reappeared in commit 427faee167bc (\"net: ipv6: introduce\nip6_dst_mtu_maybe_forward\"), which is chosen as the Fixes tag here. The\noverflow with IPV6_PMTUDISC_PROBE reproduces since its introduction in\ncommit 628a5c561890 (\"[INET]: Add IP(V6)_PMTUDISC_RPOBE\")."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"1dd562f3019019ffdf4b396570613053facda9ee","versionType":"git"},{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"1d56a00ec91f2885c64ea5b8cea18cb746b91bbb","versionType":"git"},{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"ce66352d3eb21825410af8b91db7cc4bb8e22c98","versionType":"git"},{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc","versionType":"git"},{"version":"427faee167bce4ccb0b22f6815a9ac509e31d4c3","status":"affected","lessThan":"0ae10b6be49b425827659b23bcce498f80eb7182","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/ip6_output.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.15","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","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/ipv6/ip6_output.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/1dd562f3019019ffdf4b396570613053facda9ee"},{"url":"https://git.kernel.org/stable/c/1d56a00ec91f2885c64ea5b8cea18cb746b91bbb"},{"url":"https://git.kernel.org/stable/c/ce66352d3eb21825410af8b91db7cc4bb8e22c98"},{"url":"https://git.kernel.org/stable/c/e01b7c176d9af2b7c22bb3fe12cf9a7904f99fdc"},{"url":"https://git.kernel.org/stable/c/0ae10b6be49b425827659b23bcce498f80eb7182"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T09:11:51.310Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"6.6.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"6.12.111"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"6.18.53"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"7.2.7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}