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GHSA-78M7-4XGC-XRRQ

Vulnerability from github – Published: 2026-05-01 15:30 – Updated: 2026-08-20 15:33
VLAI
Details

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

ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()

Sashiko AI-review observed:

In ip6_err_gen_icmpv6_unreach(), the skb is an outer IPv4 ICMP error packet where its cb contains an IPv4 inet_skb_parm. When skb is cloned into skb2 and passed to icmp6_send(), it uses IP6CB(skb2).

IP6CB interprets the IPv4 inet_skb_parm as an inet6_skb_parm. The cipso offset in inet_skb_parm.opt directly overlaps with dsthao in inet6_skb_parm at offset 18.

If an attacker sends a forged ICMPv4 error with a CIPSO IP option, dsthao would be a non-zero offset. Inside icmp6_send(), mip6_addr_swap() is called and uses ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO).

This would scan the inner, attacker-controlled IPv6 packet starting at that offset, potentially returning a fake TLV without checking if the remaining packet length can hold the full 18-byte struct ipv6_destopt_hao.

Could mip6_addr_swap() then perform a 16-byte swap that extends past the end of the packet data into skb_shared_info?

Should the cb array also be cleared in ip6_err_gen_icmpv6_unreach() and ip6ip6_err() to prevent this?

This patch implements the first suggestion.

I am not sure if ip6ip6_err() needs to be changed. A separate patch would be better anyway.

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-2026-43038"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-843"
    ],
    "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\nipv6: icmp: clear skb2-\u003ecb[] in ip6_err_gen_icmpv6_unreach()\n\nSashiko AI-review observed:\n\n  In ip6_err_gen_icmpv6_unreach(), the skb is an outer IPv4 ICMP error packet\n  where its cb contains an IPv4 inet_skb_parm. When skb is cloned into skb2\n  and passed to icmp6_send(), it uses IP6CB(skb2).\n\n  IP6CB interprets the IPv4 inet_skb_parm as an inet6_skb_parm. The cipso\n  offset in inet_skb_parm.opt directly overlaps with dsthao in inet6_skb_parm\n  at offset 18.\n\n  If an attacker sends a forged ICMPv4 error with a CIPSO IP option, dsthao\n  would be a non-zero offset. Inside icmp6_send(), mip6_addr_swap() is called\n  and uses ipv6_find_tlv(skb, opt-\u003edsthao, IPV6_TLV_HAO).\n\n  This would scan the inner, attacker-controlled IPv6 packet starting at that\n  offset, potentially returning a fake TLV without checking if the remaining\n  packet length can hold the full 18-byte struct ipv6_destopt_hao.\n\n  Could mip6_addr_swap() then perform a 16-byte swap that extends past the end\n  of the packet data into skb_shared_info?\n\n  Should the cb array also be cleared in ip6_err_gen_icmpv6_unreach() and\n  ip6ip6_err() to prevent this?\n\nThis patch implements the first suggestion.\n\nI am not sure if ip6ip6_err() needs to be changed.\nA separate patch would be better anyway.",
  "id": "GHSA-78m7-4xgc-xrrq",
  "modified": "2026-08-20T15:33:04Z",
  "published": "2026-05-01T15:30:37Z",
  "references": [
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      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-43038"
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      "type": "WEB",
      "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2464397"
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    {
      "type": "WEB",
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
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    {
      "type": "WEB",
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-082556.html"
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      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0452b6526b2f54b2413b9cb4ff1ea2ac542c99c7"
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      "type": "WEB",
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      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-43038.json"
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      "url": "https://access.redhat.com/errata/RHSA-2026:22940"
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      "type": "CVSS_V3"
    }
  ]
}



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