{"id":"CVE-2026-72502","state":"PUBLISHED","title":"tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)\n\nWhen MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535).\nThis is interpreted by TCP as mss_clamp, allowing the MSS to reach 65535.\n\nHowever, 0xFFFF is also used as a magic value GSO_BY_FRAGS in the kernel.\nIf a TCP packet with gso_size=0xFFFF is passed to skb_segment(), it will\nbe mistakenly treated as GSO_BY_FRAGS, leading to a NULL pointer\ndereference because local TCP packets do not use frag_list.\n\nFix this by returning min(IPV6_MAXPLEN, GSO_BY_FRAGS - 1) (65534) from\nip6_default_advmss() when MTU is large.\n\nAlso update the stale comment in ip6_default_advmss() which suggested\nthat IPV6_MAXPLEN is returned to mean \"any MSS\".","publishedAt":"2026-08-15T05:57:33.647Z","updatedAt":"2026-10-16T18:55:27.761Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"560b33b434e922ef97f9ff23aa2e909ef7aacd5c","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"21f69ac1879bb970588d5e7c12a96e6542f7c1a7","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"c0db3dc2ac323b6c4b76adede3b355a9daa6dea8","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"572fff10819dfc359298d1f774839e76a4d96f93","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"8e6214a530c03e341dc1b0a846c8f2b716b3551a","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"a210791f33345aa87187f7d7a9f3b9b7f4a28e6d","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/route.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.8","versionType":"semver"},{"version":"5.10.261","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.212","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/route.c"]}],"references":["https://git.kernel.org/stable/c/560b33b434e922ef97f9ff23aa2e909ef7aacd5c","https://git.kernel.org/stable/c/21f69ac1879bb970588d5e7c12a96e6542f7c1a7","https://git.kernel.org/stable/c/c0db3dc2ac323b6c4b76adede3b355a9daa6dea8","https://git.kernel.org/stable/c/572fff10819dfc359298d1f774839e76a4d96f93","https://git.kernel.org/stable/c/8e6214a530c03e341dc1b0a846c8f2b716b3551a","https://git.kernel.org/stable/c/d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e","https://git.kernel.org/stable/c/a210791f33345aa87187f7d7a9f3b9b7f4a28e6d","https://git.kernel.org/stable/c/2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/72xxx/CVE-2026-72502.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-72502","state":"PUBLISHED","datePublished":"2026-08-15T05:57:33.647Z","dateUpdated":"2026-10-16T18:55:27.761Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-09T03:40:39.938Z"},"containers":{"cna":{"title":"tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)\n\nWhen MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535).\nThis is interpreted by TCP as mss_clamp, allowing the MSS to reach 65535.\n\nHowever, 0xFFFF is also used as a magic value GSO_BY_FRAGS in the kernel.\nIf a TCP packet with gso_size=0xFFFF is passed to skb_segment(), it will\nbe mistakenly treated as GSO_BY_FRAGS, leading to a NULL pointer\ndereference because local TCP packets do not use frag_list.\n\nFix this by returning min(IPV6_MAXPLEN, GSO_BY_FRAGS - 1) (65534) from\nip6_default_advmss() when MTU is large.\n\nAlso update the stale comment in ip6_default_advmss() which suggested\nthat IPV6_MAXPLEN is returned to mean \"any MSS\"."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"560b33b434e922ef97f9ff23aa2e909ef7aacd5c","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"21f69ac1879bb970588d5e7c12a96e6542f7c1a7","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"c0db3dc2ac323b6c4b76adede3b355a9daa6dea8","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"572fff10819dfc359298d1f774839e76a4d96f93","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"8e6214a530c03e341dc1b0a846c8f2b716b3551a","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"a210791f33345aa87187f7d7a9f3b9b7f4a28e6d","versionType":"git"},{"version":"3953c46c3ac7eef31a9935427371c6f54a22f1ba","status":"affected","lessThan":"2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/route.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.8","versionType":"semver"},{"version":"5.10.261","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.212","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv6/route.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/560b33b434e922ef97f9ff23aa2e909ef7aacd5c"},{"url":"https://git.kernel.org/stable/c/21f69ac1879bb970588d5e7c12a96e6542f7c1a7"},{"url":"https://git.kernel.org/stable/c/c0db3dc2ac323b6c4b76adede3b355a9daa6dea8"},{"url":"https://git.kernel.org/stable/c/572fff10819dfc359298d1f774839e76a4d96f93"},{"url":"https://git.kernel.org/stable/c/8e6214a530c03e341dc1b0a846c8f2b716b3551a"},{"url":"https://git.kernel.org/stable/c/d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e"},{"url":"https://git.kernel.org/stable/c/a210791f33345aa87187f7d7a9f3b9b7f4a28e6d"},{"url":"https://git.kernel.org/stable/c/2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - Reachable from the network via IPv6 TCP: a remote peer sends a crafted SYN (MSS=65535) or connects over a large-MTU IPv6 route, causing outbound TCP GSO skbs with gso_size=0xFFFF to be software-segmented in skb_segment() during normal packet transmit.\nAC:L - The attacker controls the TCP handshake MSS option and can induce >64KB outbound segments; syzbot reproduced this reliably, and software GSO paths (loopback, veth, NETIF_F_GSO_SOFTWARE) are common in cloud/container deployments where skb_segment() is invoked.\nPR:N - No privileges are required; exploitation occurs on the pre-authentication passive-open path where the kernel accepts a remote TCP SYN and MSS option before any application-level authentication.\nUI:N - No victim user interaction is needed beyond the target system normally accepting IPv6 TCP connections and transmitting response data to the attacker-controlled peer.\nS:U - The vulnerability causes a kernel crash on the attacked host itself; it does not cross a security boundary such as a VM escape, container sandbox breakout, or IOMMU/DMA isolation bypass.\nC:N - Impact is a NULL pointer dereference in skb_segment() when gso_size equals GSO_BY_FRAGS; there is no out-of-bounds read, use-after-free, or other memory disclosure primitive.\nI:N - The bug does not corrupt or modify attacker-controlled memory; it dereferences a NULL frag_list pointer during segmentation, yielding a crash rather than a write or code-execution primitive.\nA:H - The NULL pointer dereference in skb_segment() triggers a kernel oops/panic, causing complete loss of availability for the affected system when the malicious IPv6 TCP traffic path is exercised."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-17T05:45:02.121Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"5.10.261"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"5.15.212"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"6.1.178"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"6.6.145"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"6.12.97"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"6.18.40"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-72502","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T18:51:17.494885Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T18:55:27.761Z"}}]}}}