Vulnerability-Lookup

GHSA-HVGQ-CH9F-27RQ

Vulnerability from github – Published: 2026-07-19 18:31 – Updated: 2026-07-20 15:31

Details

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

tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmpv6

Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head.

Fix this possible UAF by initializing the local variables after the skb_cow() call.

Remove skb_reset_network_header() calls which were not needed.

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-2026-63994"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-19T16:17:38Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()\n\nSashiko found that iptunnel_pmtud_build_icmp() and\niptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr()\nbefore an skb_cow() call which can reallocate skb-\u003ehead.\n\nFix this possible UAF by initializing the local variables\nafter the skb_cow() call.\n\nRemove skb_reset_network_header() calls which were not needed.",
  "id": "GHSA-hvgq-ch9f-27rq",
  "modified": "2026-07-20T15:31:54Z",
  "published": "2026-07-19T18:31:48Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63994"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43"
    }
  ],
  "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"
    }
  ]
}

CVE-2026-63994 (GCVE-0-2026-63994)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:56 – Updated: 2026-08-05 12:37

Title

tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

Summary

In the Linux kernel, the following vulnerability has been resolved: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]() Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head. Fix this possible UAF by initializing the local variables after the skb_cow() call. Remove skb_reset_network_header() calls which were not needed.

Severity

9.8 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Assigner

Linux mitre root

References

8 references

URL	Tags
https://git.kernel.org/stable/c/95b6d772bfe788331…
https://git.kernel.org/stable/c/7254aef4d1a7e18e8…
https://git.kernel.org/stable/c/bf8b3f34c37c16235…
https://git.kernel.org/stable/c/76cd9398a0470257a…
https://git.kernel.org/stable/c/50750d86a2e5266ab…
https://git.kernel.org/stable/c/6dff77899b9e9fe5d…
https://git.kernel.org/stable/c/f3f204541f280a6ec…
https://git.kernel.org/stable/c/b4bc94353050b1fa7…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f , < 95b6d772bfe788331d9742d73eaa12e113b2adc4 (git) Affected: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f , < 7254aef4d1a7e18e887af9010e2f2dc34806789b (git) Affected: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f , < bf8b3f34c37c162357138e7c0942723b8b94fed1 (git) Affected: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f , < 76cd9398a0470257ab765bdf5f358a2af2e17934 (git) Affected: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f , < 50750d86a2e5266aba0c295483b3397843198b11 (git) Affected: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f , < 6dff77899b9e9fe5d854abda3a98ad04e7229ef7 (git) Affected: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f , < f3f204541f280a6ecb04503a0d6794d93990ca43 (git) Affected: 4cb47a8644cc9eb8ec81190a50e79e6530d0297f , < b4bc94353050b1fa7b702bd4c6600710dd926cff (git)
Linux	Linux	Affected: 5.9 Unaffected: 0 , < 5.9 (semver) Unaffected: 5.10.259 , ≤ 5.10.* (semver) Unaffected: 5.15.210 , ≤ 5.15.* (semver) Unaffected: 6.1.176 , ≤ 6.1.* (semver) Unaffected: 6.6.143 , ≤ 6.6.* (semver) Unaffected: 6.12.93 , ≤ 6.12.* (semver) Unaffected: 6.18.35 , ≤ 6.18.* (semver) Unaffected: 7.0.12 , ≤ 7.0.* (semver) Unaffected: 7.1 , ≤ * (original_commit_for_fix)

Show details on NVD website

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/ip_tunnel_core.c"
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            },
            {
              "lessThan": "bf8b3f34c37c162357138e7c0942723b8b94fed1",
              "status": "affected",
              "version": "4cb47a8644cc9eb8ec81190a50e79e6530d0297f",
              "versionType": "git"
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              "status": "affected",
              "version": "5.9"
            },
            {
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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            {
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              "status": "unaffected",
              "version": "5.10.259",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.210",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.176",
              "versionType": "semver"
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            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.143",
              "versionType": "semver"
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            {
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              "versionType": "semver"
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.35",
              "versionType": "semver"
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              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
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        }
      ],
      "cpeApplicability": [
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                  "versionStartIncluding": "5.9",
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                },
                {
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                  "vulnerable": true
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "5.9",
                  "vulnerable": true
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        {
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()\n\nSashiko found that iptunnel_pmtud_build_icmp() and\niptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr()\nbefore an skb_cow() call which can reallocate skb-\u003ehead.\n\nFix this possible UAF by initializing the local variables\nafter the skb_cow() call.\n\nRemove skb_reset_network_header() calls which were not needed."
        }
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            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
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              "lang": "en",
              "value": "AV:N - The bug is reached when remotely injected VXLAN/GENEVE UDP packets traverse a bridged/OVS overlay and fail PMTU checks during encapsulation transmit, the same network path previously demonstrated in CVE-2023-53600 via vxlan_xmit through bridge forwarding.\nAC:L - An attacker can reliably send oversized DF-marked inner IP packets over the overlay to force PMTU ICMP generation, and can influence skb_cow() reallocation through bridge flooding/multicast cloning or headroom pressure; no uncontrollable victim state is required.\nPR:N - Exploitation requires no privileges on the victim host; any remote entity that can send VXLAN/GENEVE traffic to a VTEP with a bridged tunnel interface (standard cloud/SDN deployment) can reach the vulnerable code without authentication.\nUI:N - Triggering is fully automatic during kernel packet forwarding and tunnel encapsulation; no victim user action is needed beyond normal network operation of an overlay endpoint.\nS:U - Impact is confined to kernel memory on the affected host (UAF read/crash/potential escalation); it does not inherently cross VM, container, or IOMMU security boundaries.\nC:H - Stale ip_hdr/ipv6_hdr pointers cause reads from freed slab memory; leaked values are incorporated into ICMP error IP headers that are sent back to the attacker, constituting arbitrary kernel heap content disclosure.\nI:H - Use-after-free on skb header memory is a heap corruption primitive that can be developed into controlled writes or code execution via heap grooming, consistent with kernel UAF severity guidance.\nA:H - Dereferencing freed skb head memory during ICMP construction can cause kernel oops/panic and denial of service, as with other confirmed bugs in this same code path."
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        "dateUpdated": "2026-08-05T12:37:58.389Z",
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          "url": "https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff"
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      "title": "tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()",
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    "dateReserved": "2026-07-19T07:54:57.026Z",
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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GHSA-HVGQ-CH9F-27RQ

CVE-2026-63994 (GCVE-0-2026-63994)

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