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GHSA-VC8F-29MH-24XV

Vulnerability from github – Published: 2026-09-04 18:31 – Updated: 2026-09-04 18:31
VLAI
Details

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.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-80793"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-04T16:18:05Z",
    "severity": null
  },
  "details": "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.",
  "id": "GHSA-vc8f-29mh-24xv",
  "modified": "2026-09-04T18:31:26Z",
  "published": "2026-09-04T18:31:26Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80793"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3556beb8ca86677af2aca5bfbed6f8e790fccc83"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/36e0741833bd823866f8cb9f112f37cea1a70b60"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/515b6816ba0c12d8415c88e5f41e6ec029e35cfa"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/74ce7389f8f562d39015f59a00ef7ad6acd37803"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a716a64a4ba68cd46f2745fba2b1099fe8e0aa59"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b0ea911453ce7210e8200a07a94d2458bd1e6430"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c0726f0caf8c6b3208552949e17d23634a2f3129"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c8a74adccaf028223054633b532593101dfcc581"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d9d1a676b033acabf8e5645f730486d1f8204a3f"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}



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