CVE-2026-63992 (GCVE-0-2026-63992)
Vulnerability from cvelistv5
Published
2026-07-19 14:56
Modified
2026-08-05 12:37
Severity ?
9.1 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: tunnels: do not assume transport header in iptunnel_pmtud_check_icmp() In some cases, iptunnel_pmtud_check_icmp() can be called while skb transport header is not set. This triggers an out-of-bound access, because (typeof(skb->transport_header))~0U is 65535. Access the icmp header based on IPv4 network header, after making sure icmp->type is present in skb linear part. Note that iptunnel_pmtud_check_icmpv6()) is fine.
References
Impacted products
Vendor Product Version
Linux Linux Version: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f
Version: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f
Version: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f
Version: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f
Version: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f
Version: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f
Version: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f
Version: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f
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{
  "containers": {
    "cna": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/ip_tunnel_core.c"
          ],
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          "vendor": "Linux",
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "5.9"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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              "version": "5.10.259",
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              "version": "5.15.210",
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            },
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              "status": "unaffected",
              "version": "6.1.176",
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              "version": "6.6.143",
              "versionType": "semver"
            },
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              "status": "unaffected",
              "version": "6.12.93",
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            },
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              "status": "unaffected",
              "version": "6.18.35",
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            },
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              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.259",
                  "versionStartIncluding": "5.9",
                  "vulnerable": true
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                {
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                  "versionStartIncluding": "5.9",
                  "vulnerable": true
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                {
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                  "versionEndExcluding": "7.1",
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                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntunnels: do not assume transport header in iptunnel_pmtud_check_icmp()\n\nIn some cases, iptunnel_pmtud_check_icmp() can be called while\nskb transport header is not set.\n\nThis triggers an out-of-bound access, because\n(typeof(skb-\u003etransport_header))~0U is 65535.\n\nAccess the icmp header based on IPv4 network header,\nafter making sure icmp-\u003etype is present in skb linear part.\n\nNote that iptunnel_pmtud_check_icmpv6()) is fine."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.1,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The vulnerable code runs on the VXLAN/GENEVE transmit path when processing remotely received UDP-encapsulated tunnel traffic (or L2 frames forwarded through a bridge port), which is reachable by sending crafted packets over the network to the victim VTEP.\nAC:L - The attacker fully controls the inner IPv4 header fields (DF bit, length, addresses) and can reliably craft oversized packets that exceed the tunnel-adjusted PMTU on bridge-port tunnel devices without depending on race timing or uncontrollable system state.\nPR:N - Exploitation requires only the ability to send network packets to a host with VXLAN/GENEVE bridged; no local account, authentication, or capabilities on the victim are needed.\nUI:N - No victim user action is required; the kernel processes attacker-supplied packets automatically through the tunnel receive, bridge forward, and re-encapsulation path.\nS:U - The out-of-bounds read and resulting kernel oops occur within the kernel network stack on the same host; there is no crossing of a VM, container, or IOMMU security boundary beyond standard kernel memory safety failure.\nC:H - Reading through `icmp_hdr(skb)` when `transport_header` is unset causes an out-of-bounds read at `skb-\u003ehead + 65535`, potentially disclosing adjacent kernel memory beyond the skb buffer before any bounds checking occurs.\nI:N - The flaw is an out-of-bounds read of the ICMP type field; it does not directly modify or write kernel memory, though it may cause a kernel fault.\nA:H - The invalid pointer dereference at offset 65535 can trigger a kernel oops or panic when accessing unmapped memory, causing denial of service on the affected host."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:37:55.661Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/5a92cb45e34749865d03daf8d3500f77b5f6644c"
        },
        {
          "url": "https://git.kernel.org/stable/c/c7b7ec3e69e673c0d6b57f74d21da50c485c598e"
        },
        {
          "url": "https://git.kernel.org/stable/c/7f4f7efe7f30edd29c4988de01728bf2398217e4"
        },
        {
          "url": "https://git.kernel.org/stable/c/e917d0c69f01af2bb4fbea2b66d560a53b3ac7ec"
        },
        {
          "url": "https://git.kernel.org/stable/c/a096b6e34f602950af9a2b0856cd93a5f4c276d7"
        },
        {
          "url": "https://git.kernel.org/stable/c/43368636c663cff6e59dde93cf4b8e43ac28eb93"
        },
        {
          "url": "https://git.kernel.org/stable/c/cb549df9ce4ee15c9d5b19ddab12cf2128e4313c"
        },
        {
          "url": "https://git.kernel.org/stable/c/509323077ef79a26ba0c60bb556e45c12c398b2d"
        }
      ],
      "title": "tunnels: do not assume transport header in iptunnel_pmtud_check_icmp()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63992",
    "datePublished": "2026-07-19T14:56:12.528Z",
    "dateReserved": "2026-07-19T07:54:57.025Z",
    "dateUpdated": "2026-08-05T12:37:55.661Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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