CVE-2026-80793 (GCVE-0-2026-80793)
Vulnerability from cvelistv5
Published
2026-09-04 15:13
Modified
2026-10-19 08:43
Severity ?
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
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      "descriptions": [
        {
          "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": {
        "dateUpdated": "2026-10-19T08:43:46.499Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a716a64a4ba68cd46f2745fba2b1099fe8e0aa59"
        },
        {
          "url": "https://git.kernel.org/stable/c/515b6816ba0c12d8415c88e5f41e6ec029e35cfa"
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        {
          "url": "https://git.kernel.org/stable/c/74ce7389f8f562d39015f59a00ef7ad6acd37803"
        },
        {
          "url": "https://git.kernel.org/stable/c/b0ea911453ce7210e8200a07a94d2458bd1e6430"
        },
        {
          "url": "https://git.kernel.org/stable/c/36e0741833bd823866f8cb9f112f37cea1a70b60"
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        {
          "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"
        }
      ],
      "title": "ipv4: reject undersized MTUs in ip_do_fragment()",
      "x_generator": {
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  "cveMetadata": {
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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": "2026-10-19T08:43:46.499Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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