{"id":"CVE-2026-63994","state":"PUBLISHED","title":"tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()","description":"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->head.\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.","publishedAt":"2026-07-19T14:56:13.896Z","updatedAt":"2026-10-19T20:18:01.494Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"95b6d772bfe788331d9742d73eaa12e113b2adc4","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"7254aef4d1a7e18e887af9010e2f2dc34806789b","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"bf8b3f34c37c162357138e7c0942723b8b94fed1","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"76cd9398a0470257ab765bdf5f358a2af2e17934","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"50750d86a2e5266aba0c295483b3397843198b11","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"6dff77899b9e9fe5d854abda3a98ad04e7229ef7","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"f3f204541f280a6ecb04503a0d6794d93990ca43","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"b4bc94353050b1fa7b702bd4c6600710dd926cff","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/ip_tunnel_core.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.9","versionType":"semver"},{"version":"5.10.259","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.210","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.176","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.143","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.93","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.35","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.12","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/ip_tunnel_core.c"]}],"references":["https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4","https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b","https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1","https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934","https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11","https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7","https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43","https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff"],"weaknesses":["CWE-416"],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/63xxx/CVE-2026-63994.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63994","state":"PUBLISHED","datePublished":"2026-07-19T14:56:13.896Z","dateUpdated":"2026-10-19T20:18:01.494Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-19T07:54:57.026Z"},"containers":{"cna":{"title":"tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()","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->head.\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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"95b6d772bfe788331d9742d73eaa12e113b2adc4","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"7254aef4d1a7e18e887af9010e2f2dc34806789b","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"bf8b3f34c37c162357138e7c0942723b8b94fed1","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"76cd9398a0470257ab765bdf5f358a2af2e17934","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"50750d86a2e5266aba0c295483b3397843198b11","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"6dff77899b9e9fe5d854abda3a98ad04e7229ef7","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"f3f204541f280a6ecb04503a0d6794d93990ca43","versionType":"git"},{"version":"4cb47a8644cc9eb8ec81190a50e79e6530d0297f","status":"affected","lessThan":"b4bc94353050b1fa7b702bd4c6600710dd926cff","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/ip_tunnel_core.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.9","versionType":"semver"},{"version":"5.10.259","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.210","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.176","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.143","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.93","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.35","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.12","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/ip_tunnel_core.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4"},{"url":"https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b"},{"url":"https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1"},{"url":"https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934"},{"url":"https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11"},{"url":"https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7"},{"url":"https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43"},{"url":"https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"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 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ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-63994","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:34:51.504885Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-416","lang":"en","type":"CWE","description":"CWE-416 Use After Free"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T20:18:01.494Z"}}]}}}