GHSA-66J4-C66H-JM7X

Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

ipv4: fib: Don't ignore error route in local/main tables.

When CONFIG_IP_MULTIPLE_TABLES is enabled but no rule is added, fib_lookup() performs route lookup directly on two tables.

Since the first lookup does not properly bail out, the result of an error route in the merged local/main table could be overwritten by another route in the default table:

# unshare -n # ip link set lo up # ip route add 192.168.0.0/24 dev lo table 253 # ip route add unreachable 192.168.0.0/24 # ip route get 192.168.0.1 192.168.0.1 dev lo table default uid 0 cache

Once a random rule is added, the error route is respected:

# ip rule add table 0 # ip rule del table 0 # ip route get 192.168.0.1 RTNETLINK answers: No route to host

Let's fix the inconsistent behaviour.

Severity
10.0 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Show details on source website
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{
  "affected": [],
  "aliases": [
    "CVE-2026-72421"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-15T06:22:15Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: fib: Don\u0027t ignore error route in local/main tables.\n\nWhen CONFIG_IP_MULTIPLE_TABLES is enabled but no rule is added,\nfib_lookup() performs route lookup directly on two tables.\n\nSince the first lookup does not properly bail out, the result\nof an error route in the merged local/main table could be\noverwritten by another route in the default table:\n\n  # unshare -n\n  # ip link set lo up\n  # ip route add 192.168.0.0/24 dev lo table 253\n  # ip route add unreachable 192.168.0.0/24\n  # ip route get 192.168.0.1\n  192.168.0.1 dev lo table default uid 0\n      cache \u003clocal\u003e\n\nOnce a random rule is added, the error route is respected:\n\n  # ip rule add table 0\n  # ip rule del table 0\n  # ip route get 192.168.0.1\n  RTNETLINK answers: No route to host\n\nLet\u0027s fix the inconsistent behaviour.",
  "id": "GHSA-66j4-c66h-jm7x",
  "modified": "2026-08-17T06:33:29Z",
  "published": "2026-08-15T06:32:23Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72421"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/49eaf1403201357762d745a35882fb734107d763"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5ae18d87a45698e8244d0fcba64c658c35a7dd3d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/828fad4fd418bcdb9f5d66fec0d184c52a85ec31"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9127589aabdee588278e8d0d0bd3709a760a92c8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a29e95fbc51e8a1b932773fd0e259b2080881443"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a668fa160247d7bbe921548cb845f607b8b9305f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b72f0db64205d9ce462038ba995d5d31eff32dc1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fd25996f57a95d56bc568c89b4921edcf334b7d8"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ]
}



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