GHSA-G5VP-298M-R34Q

Vulnerability from github – Published: 2026-06-24 18:32 – Updated: 2026-06-24 18:32
VLAI
Details

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

nexthop: fix IPv6 route referencing IPv4 nexthop

syzbot reported a panic [1] [2].

When an IPv6 nexthop is replaced with an IPv4 nexthop, the has_v4 flag of all groups containing this nexthop is not updated. This is because nh_group_v4_update is only called when replacing AF_INET to AF_INET6, but the reverse direction (AF_INET6 to AF_INET) is missed.

This allows a stale has_v4=false to bypass fib6_check_nexthop, causing IPv6 routes to be attached to groups that effectively contain only AF_INET members. Subsequent route lookups then call nexthop_fib6_nh() which returns NULL for the AF_INET member, leading to a NULL pointer dereference.

Fix by calling nh_group_v4_update whenever the family changes, not just AF_INET to AF_INET6.

Reproducer: # AF_INET6 blackhole ip -6 nexthop add id 1 blackhole # group with has_v4=false ip nexthop add id 100 group 1 # replace with AF_INET (no -6), has_v4 stays false ip nexthop replace id 1 blackhole # pass stale has_v4 check ip -6 route add 2001:db8::/64 nhid 100 # panic ping -6 2001:db8::1

[1] https://syzkaller.appspot.com/bug?id=e17283eb2f8dcf3dd9b47fe6f67a95f71faadad0 [2] https://syzkaller.appspot.com/bug?id=8699b6ae54c9f35837d925686208402949e12ef3

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{
  "affected": [],
  "aliases": [
    "CVE-2026-53012"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-24T17:17:12Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnexthop: fix IPv6 route referencing IPv4 nexthop\n\nsyzbot reported a panic [1] [2].\n\nWhen an IPv6 nexthop is replaced with an IPv4 nexthop, the has_v4 flag\nof all groups containing this nexthop is not updated. This is because\nnh_group_v4_update is only called when replacing AF_INET to AF_INET6,\nbut the reverse direction (AF_INET6 to AF_INET) is missed.\n\nThis allows a stale has_v4=false to bypass fib6_check_nexthop, causing\nIPv6 routes to be attached to groups that effectively contain only AF_INET\nmembers. Subsequent route lookups then call nexthop_fib6_nh() which\nreturns NULL for the AF_INET member, leading to a NULL pointer\ndereference.\n\nFix by calling nh_group_v4_update whenever the family changes, not just\nAF_INET to AF_INET6.\n\nReproducer:\n\t# AF_INET6 blackhole\n\tip -6 nexthop add id 1 blackhole\n\t# group with has_v4=false\n\tip nexthop add id 100 group 1\n\t# replace with AF_INET (no -6), has_v4 stays false\n\tip nexthop replace id 1 blackhole\n\t# pass stale has_v4 check\n\tip -6 route add 2001:db8::/64 nhid 100\n\t# panic\n\tping -6 2001:db8::1\n\n[1] https://syzkaller.appspot.com/bug?id=e17283eb2f8dcf3dd9b47fe6f67a95f71faadad0\n[2] https://syzkaller.appspot.com/bug?id=8699b6ae54c9f35837d925686208402949e12ef3",
  "id": "GHSA-g5vp-298m-r34q",
  "modified": "2026-06-24T18:32:44Z",
  "published": "2026-06-24T18:32:43Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53012"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/29c95185ba32b621fbc3800fb86e7dc3edf5c2be"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/613c8f4a501421dd258b07ea614205d4e16ec845"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6275796f22bb382f3e9aa58ed0b4ef7bdad78cb8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9c2d6770a5f4545a307eb66979bef7656a34d621"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/aaac3bed034239e1d75732211d9b05f30b0b4f35"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ad85961004fd4bd2f31209ac4b07612c6cefb9e7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b3b7e850e1541f0520c4a12ec884255c30427ff6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ceffe81a0be92afc0cd1340bc8ca46559cce9bb4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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