GHSA-P2WF-QJ6M-X5FG

Vulnerability from github – Published: 2026-05-01 15:30 – Updated: 2026-05-03 09:33
VLAI?
Details

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

ip6_tunnel: clear skb2->cb[] in ip4ip6_err()

Oskar Kjos reported the following problem.

ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the IPv6 receive path as struct inet6_skb_parm. icmp_send() passes IPCB(skb2) to __ip_options_echo(), which interprets that cb[] region as struct inet_skb_parm (IPv4). The layouts differ: inet6_skb_parm.nhoff at offset 14 overlaps inet_skb_parm.opt.rr, producing a non-zero rr value. __ip_options_echo() then reads optlen from attacker-controlled packet data at sptr[rr+1] and copies that many bytes into dopt->__data, a fixed 40-byte stack buffer (IP_OPTIONS_DATA_FIXED_SIZE).

To fix this we clear skb2->cb[], as suggested by Oskar Kjos.

Also add minimal IPv4 header validation (version == 4, ihl >= 5).

Severity ?
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-43037"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-787"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-01T15:16:48Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nip6_tunnel: clear skb2-\u003ecb[] in ip4ip6_err()\n\nOskar Kjos reported the following problem.\n\nip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written\nby the IPv6 receive path as struct inet6_skb_parm. icmp_send() passes\nIPCB(skb2) to __ip_options_echo(), which interprets that cb[] region\nas struct inet_skb_parm (IPv4). The layouts differ: inet6_skb_parm.nhoff\nat offset 14 overlaps inet_skb_parm.opt.rr, producing a non-zero rr\nvalue. __ip_options_echo() then reads optlen from attacker-controlled\npacket data at sptr[rr+1] and copies that many bytes into dopt-\u003e__data,\na fixed 40-byte stack buffer (IP_OPTIONS_DATA_FIXED_SIZE).\n\nTo fix this we clear skb2-\u003ecb[], as suggested by Oskar Kjos.\n\nAlso add minimal IPv4 header validation (version == 4, ihl \u003e= 5).",
  "id": "GHSA-p2wf-qj6m-x5fg",
  "modified": "2026-05-03T09:33:10Z",
  "published": "2026-05-01T15:30:37Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-43037"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1063515ce15ff31065c4e7f8265f4c2fd3c54876"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2edfa31769a4add828a7e604b21cb82aaaa05925"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4a622658f384b03560834cbe8ffcfe69a278f7c8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a0c4ce9900a108eaf55d0f3b399cb55999647d39"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d6621f60192fe10c047a4487be42a6f4c150707f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ea9f65b27c8404e164848ebff1443310fd187629"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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