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ipv4: reject undersized MTUs in ip_do_fragment()

Type: advisorySource: Official CVE List1 source record

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.

Announced Group revision 1
Original source ↗

CVE-2026-80793

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-80793

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "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"
      }
    ],
    "programFiles": [
      "net/ipv4/ip_output.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "2.6.12"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "2.6.12",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.10.267",
        "versionType": "semver",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.15.218",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.185",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.154",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.106",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.47",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.1.11",
        "versionType": "semver",
        "lessThanOrEqual": "7.1.*"
      },
      {
        "status": "unaffected",
        "version": "7.2.1",
        "versionType": "semver",
        "lessThanOrEqual": "7.2.*"
      },
      {
        "status": "unaffected",
        "version": "7.3",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "net/ipv4/ip_output.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-80793

Source reference: /cveMetadata/cveId

Publisher severity

No explicit severity was provided.

Event
#34809 · Revision 1
Added to Heist Feed
Publisher date
Read the original announcement

Revision history

  1. CVE-2026-80793 · Revision 1Source updated