{"id":"CVE-2026-80793","title":"ipv4: reject undersized MTUs in ip_do_fragment()","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: reject undersized MTUs in ip_do_fragment()\n\nip_do_fragment() subtracts the IPv4 header length from the effective\nMTU and passes the resulting payload MTU to ip_fr…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < a716a64a4ba68cd46f2745fba2b1099fe8e0aa59","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 515b6816ba0c12d8415c88e5f41e6ec029e35cfa","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 74ce7389f8f562d39015f59a00ef7ad6acd37803","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < b0ea911453ce7210e8200a07a94d2458bd1e6430","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 36e0741833bd823866f8cb9f112f37cea1a70b60","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < d9d1a676b033acabf8e5645f730486d1f8204a3f","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 3556beb8ca86677af2aca5bfbed6f8e790fccc83","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c8a74adccaf028223054633b532593101dfcc581","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c0726f0caf8c6b3208552949e17d23634a2f3129","Linux 2.6.12"],"published":"2026-09-04","updated":"2026-10-19","sourceUpdated":"2026-10-19T08:43:46.499Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-80793","references":[{"url":"https://git.kernel.org/stable/c/a716a64a4ba68cd46f2745fba2b1099fe8e0aa59"},{"url":"https://git.kernel.org/stable/c/515b6816ba0c12d8415c88e5f41e6ec029e35cfa"},{"url":"https://git.kernel.org/stable/c/74ce7389f8f562d39015f59a00ef7ad6acd37803"},{"url":"https://git.kernel.org/stable/c/b0ea911453ce7210e8200a07a94d2458bd1e6430"},{"url":"https://git.kernel.org/stable/c/36e0741833bd823866f8cb9f112f37cea1a70b60"},{"url":"https://git.kernel.org/stable/c/d9d1a676b033acabf8e5645f730486d1f8204a3f"},{"url":"https://git.kernel.org/stable/c/3556beb8ca86677af2aca5bfbed6f8e790fccc83"},{"url":"https://git.kernel.org/stable/c/c8a74adccaf028223054633b532593101dfcc581"},{"url":"https://git.kernel.org/stable/c/c0726f0caf8c6b3208552949e17d23634a2f3129"}],"tags":["cve.org"],"epss":0.00195,"epssPercentile":0.08586,"ingestedAt":"2026-10-19T09:16:01.530Z","slug":"CVE-2026-80793","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nipv4: reject undersized MTUs in ip_do_fragment()\n\nip_do_fragment() subtracts the IPv4 header length from the effective\nMTU and passes the resulting payload MTU to ip_frag_next().\n\nIf the effective MTU is smaller than hlen + 8, ip_frag_next() rounds\nthe fragment payload length down to zero. The fragmentation state then\nnever makes forward progress: state->left, state->ptr and state->offset\nstay unchanged while ip_do_fragment() keeps allocating and transmitting\nheader-only fragments until the softlockup detector fires.\n\nThis is reproducible with a route installed using \"mtu lock 20\", but it\nis also reproducible without route MTU lock, for example by forwarding a\npacket to a device whose MTU is 20.\n\nFix it in ip_do_fragment() by rejecting mtu < hlen + 8 with -EMSGSIZE,\nmatching the existing IPv6 fragmentation check.\n\n## Affected\n\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < a716a64a4ba68cd46f2745fba2b1099fe8e0aa59`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 515b6816ba0c12d8415c88e5f41e6ec029e35cfa`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 74ce7389f8f562d39015f59a00ef7ad6acd37803`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < b0ea911453ce7210e8200a07a94d2458bd1e6430`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 36e0741833bd823866f8cb9f112f37cea1a70b60`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < d9d1a676b033acabf8e5645f730486d1f8204a3f`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 3556beb8ca86677af2aca5bfbed6f8e790fccc83`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c8a74adccaf028223054633b532593101dfcc581`\n- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c0726f0caf8c6b3208552949e17d23634a2f3129`\n- `Linux 2.6.12`\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":[]}