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CVE-2026-80793 (GCVE-0-2026-80793)

Vulnerability from cvelistv5 – Published: 2026-09-04 15:13 – Updated: 2026-09-04 15:13
VLAI
Title
ipv4: reject undersized MTUs in ip_do_fragment()
Summary
In the Linux kernel, the following vulnerability has been resolved: ipv4: reject undersized MTUs in ip_do_fragment() ip_do_fragment() subtracts the IPv4 header length from the effective MTU and passes the resulting payload MTU to ip_frag_next(). If the effective MTU is smaller than hlen + 8, ip_frag_next() rounds the fragment payload length down to zero. The fragmentation state then never makes forward progress: state->left, state->ptr and state->offset stay unchanged while ip_do_fragment() keeps allocating and transmitting header-only fragments until the softlockup detector fires. This is reproducible with a route installed using "mtu lock 20", but it is also reproducible without route MTU lock, for example by forwarding a packet to a device whose MTU is 20. Fix it in ip_do_fragment() by rejecting mtu < hlen + 8 with -EMSGSIZE, matching the existing IPv6 fragmentation check.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < a716a64a4ba68cd46f2745fba2b1099fe8e0aa59 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 515b6816ba0c12d8415c88e5f41e6ec029e35cfa (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 74ce7389f8f562d39015f59a00ef7ad6acd37803 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < b0ea911453ce7210e8200a07a94d2458bd1e6430 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 36e0741833bd823866f8cb9f112f37cea1a70b60 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < d9d1a676b033acabf8e5645f730486d1f8204a3f (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 3556beb8ca86677af2aca5bfbed6f8e790fccc83 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < c8a74adccaf028223054633b532593101dfcc581 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < c0726f0caf8c6b3208552949e17d23634a2f3129 (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 5.10.267 , ≤ 5.10.* (semver)
Unaffected: 5.15.218 , ≤ 5.15.* (semver)
Unaffected: 6.1.185 , ≤ 6.1.* (semver)
Unaffected: 6.6.154 , ≤ 6.6.* (semver)
Unaffected: 6.12.106 , ≤ 6.12.* (semver)
Unaffected: 6.18.47 , ≤ 6.18.* (semver)
Unaffected: 7.1.11 , ≤ 7.1.* (semver)
Unaffected: 7.2.1 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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          "lang": "en",
          "value": "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_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-\u003eleft, state-\u003eptr and state-\u003eoffset\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 \u003c hlen + 8 with -EMSGSIZE,\nmatching the existing IPv6 fragmentation check."
        }
      ],
      "providerMetadata": {
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        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/a716a64a4ba68cd46f2745fba2b1099fe8e0aa59"
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          "url": "https://git.kernel.org/stable/c/515b6816ba0c12d8415c88e5f41e6ec029e35cfa"
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          "url": "https://git.kernel.org/stable/c/3556beb8ca86677af2aca5bfbed6f8e790fccc83"
        },
        {
          "url": "https://git.kernel.org/stable/c/c8a74adccaf028223054633b532593101dfcc581"
        },
        {
          "url": "https://git.kernel.org/stable/c/c0726f0caf8c6b3208552949e17d23634a2f3129"
        }
      ],
      "title": "ipv4: reject undersized MTUs in ip_do_fragment()",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-80793",
    "datePublished": "2026-09-04T15:13:05.814Z",
    "dateReserved": "2026-08-26T14:34:25.793Z",
    "dateUpdated": "2026-09-04T15:13:05.814Z",
    "state": "PUBLISHED"
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      "date": "2026-09-15",
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      "product_status:known_affected": "1",
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      "title": "ipv4: reject undersized MTUs in ip_do_fragment()",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-80793.json",
      "version": "2"
    },
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The fragmentation state then\\nnever makes forward progress: state-\u003eleft, state-\u003eptr and state-\u003eoffset\\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 \u003c hlen + 8 with -EMSGSIZE,\\nmatching the existing IPv6 fragmentation check.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"net/ipv4/ip_output.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"a716a64a4ba68cd46f2745fba2b1099fe8e0aa59\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"515b6816ba0c12d8415c88e5f41e6ec029e35cfa\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"74ce7389f8f562d39015f59a00ef7ad6acd37803\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"b0ea911453ce7210e8200a07a94d2458bd1e6430\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"36e0741833bd823866f8cb9f112f37cea1a70b60\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"d9d1a676b033acabf8e5645f730486d1f8204a3f\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"3556beb8ca86677af2aca5bfbed6f8e790fccc83\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"c8a74adccaf028223054633b532593101dfcc581\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2\",\"lessThan\":\"c0726f0caf8c6b3208552949e17d23634a2f3129\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"net/ipv4/ip_output.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"2.6.12\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"2.6.12\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.10.267\",\"lessThanOrEqual\":\"5.10.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.218\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.1.185\",\"lessThanOrEqual\":\"6.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.154\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.106\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.47\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1.11\",\"lessThanOrEqual\":\"7.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2.1\",\"lessThanOrEqual\":\"7.2.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.3-rc1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/3556beb8ca86677af2aca5bfbed6f8e790fccc83\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/36e0741833bd823866f8cb9f112f37cea1a70b60\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/515b6816ba0c12d8415c88e5f41e6ec029e35cfa\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/74ce7389f8f562d39015f59a00ef7ad6acd37803\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a716a64a4ba68cd46f2745fba2b1099fe8e0aa59\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/b0ea911453ce7210e8200a07a94d2458bd1e6430\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/c0726f0caf8c6b3208552949e17d23634a2f3129\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/c8a74adccaf028223054633b532593101dfcc581\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/d9d1a676b033acabf8e5645f730486d1f8204a3f\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-10T01:51:31Z",
      "cve": "CVE-2026-80793",
      "id": "CVE-2026-80793",
      "initial_release_date": "2026-09-05T00:27:16Z",
      "product_status:known_affected": "341",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-80793",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-80793.json",
      "version": "4"
    }
  }
}



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