CVE-2026-43038 (GCVE-0-2026-43038)
Vulnerability from cvelistv5
Published
2026-05-01 14:15
Modified
2026-05-03 05:46
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: ca15a078bd907df5fc1c009477869c5cbde3b753
Version: ca15a078bd907df5fc1c009477869c5cbde3b753
Version: ca15a078bd907df5fc1c009477869c5cbde3b753
Version: ca15a078bd907df5fc1c009477869c5cbde3b753
Version: ca15a078bd907df5fc1c009477869c5cbde3b753
Version: ca15a078bd907df5fc1c009477869c5cbde3b753
Version: ca15a078bd907df5fc1c009477869c5cbde3b753
Version: ca15a078bd907df5fc1c009477869c5cbde3b753
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/icmp.c"
          ],
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              "lessThanOrEqual": "*",
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              "version": "7.0",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "cpeMatch": [
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-03T05:46:17.465Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/c438ba010171b70bad22fc18b1d5bdc3627476e8"
        },
        {
          "url": "https://git.kernel.org/stable/c/0452b6526b2f54b2413b9cb4ff1ea2ac542c99c7"
        },
        {
          "url": "https://git.kernel.org/stable/c/a4437faf135da293d16fcc4cc607316742bd0ebb"
        },
        {
          "url": "https://git.kernel.org/stable/c/3d5127d998de617b130aae96b138dba22ac6a8a7"
        },
        {
          "url": "https://git.kernel.org/stable/c/e41953e7d118e2702bcb217879c173d9d1d3cd4e"
        },
        {
          "url": "https://git.kernel.org/stable/c/a2edbb6393972a02114b6003953a5cef3104fada"
        },
        {
          "url": "https://git.kernel.org/stable/c/1ceeebd5bd6d855b17a5df625109bfe29129d7cf"
        },
        {
          "url": "https://git.kernel.org/stable/c/86ab3e55673a7a49a841838776f1ab18d23a67b5"
        }
      ],
      "title": "ipv6: icmp: clear skb2-\u003ecb[] in ip6_err_gen_icmpv6_unreach()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-43038",
    "datePublished": "2026-05-01T14:15:35.986Z",
    "dateReserved": "2026-05-01T14:12:55.978Z",
    "dateUpdated": "2026-05-03T05:46:17.465Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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