CVE-2026-63994 (GCVE-0-2026-63994)
Vulnerability from cvelistv5 – Published: 2026-07-19 14:56 – Updated: 2026-08-05 12:37
VLAI
EPSS
VEX
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)
Assigner
References
8 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| 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) |
guessed | |
| 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) |
guessed |
{
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"programFiles": [
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},
{
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"version": "6.1.176",
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},
{
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},
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{
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"version": "7.0.12",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "7.1",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
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"nodes": [
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"descriptions": [
{
"lang": "en",
"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."
}
],
"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"
},
"scenarios": [
{
"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."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-05T12:37:58.389Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
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"references": [
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{
"url": "https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b"
},
{
"url": "https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1"
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{
"url": "https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934"
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{
"url": "https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11"
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},
{
"url": "https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff"
}
],
"title": "tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()",
"x_generator": {
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"assignerShortName": "Linux",
"cveId": "CVE-2026-63994",
"datePublished": "2026-07-19T14:56:13.896Z",
"dateReserved": "2026-07-19T07:54:57.026Z",
"dateUpdated": "2026-08-05T12:37:58.389Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
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"date": "2026-09-29",
"epss": "0.00755",
"percentile": "0.53306"
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"nvd": {
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{
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{
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{
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}
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],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"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."
}
],
"id": "CVE-2026-63994",
"lastModified": "2026-07-30T14:51:11.223",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "HIGH",
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"exploitabilityScore": 3.9,
"impactScore": 5.9,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
}
]
},
"published": "2026-07-19T16:17:38.943",
"references": [
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"url": "https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11"
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},
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},
{
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}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Awaiting Analysis"
}
},
"redhat_vex": {
"aggregate_severity": "Important",
"current_release_date": "2026-09-14T17:13:54+00:00",
"cve": "CVE-2026-63994",
"id": "CVE-2026-63994",
"initial_release_date": "2026-07-19T00:00:00+00:00",
"product_status:known_affected": "232",
"product_status:known_not_affected": "28",
"product_status:under_investigation": "14",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63994.json",
"version": "3"
},
"suse_vex": {
"aggregate_severity": "important",
"current_release_date": "2026-09-10T16:48:33Z",
"cve": "CVE-2026-63994",
"id": "CVE-2026-63994",
"initial_release_date": "2026-07-21T13:01:58Z",
"product_status:first_fixed": "2",
"product_status:known_affected": "473",
"product_status:known_not_affected": "121",
"product_status:recommended": "442",
"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2026-63994",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-63994.json",
"version": "18"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
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.
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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.
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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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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