{"id":"CVE-2026-80634","state":"PUBLISHED","title":"netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag\n\nThe DEV_PATH_BR_VLAN_UNTAG case post-decrements info->num_encaps\ninside WARN_ON_ONCE(). num_encaps is u8, so if it's already 0 the\ndecrement still happens and wraps it to 255. The break only leaves\nthe inner switch -- a later path entry can set info->indev back to\na real device, and we end up returning with num_encaps == 255.\n\nnft_dev_forward_path() then walks info.encap[] (size 2) up to\nnum_encaps, which means an OOB stack read and a bogus count copied\ninto the route descriptor.\n\nShould only happen on a malformed bridge path stack, hence the WARN,\nbut worth handling sanely. Move the decrement out of the WARN.\n\n[ While at this, remove the WARN_ON_ONCE since this can only happen\n  with a buggy bridge path stack --pablo ].","publishedAt":"2026-08-28T06:48:49.022Z","updatedAt":"2026-10-30T12:30:48.907Z","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":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"9a4e3a9017ba3da2de187b72ed6545641a0d0a84","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"1b52aeb40c9f04bf50eeb4ea09142139d163e239","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"ee8440bb000fff4ef8acbfc99652851e9ca0a35b","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"547ea9f567498e4accc89e7816264f15a1a0629f","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"2f55fa28011c97d6495d5787808db10a8c2d690d","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"e052f920773b73be49eb4d8702a9f85de7464363","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nf_flow_table_path.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.13","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nf_flow_table_path.c"]}],"references":["https://git.kernel.org/stable/c/9a4e3a9017ba3da2de187b72ed6545641a0d0a84","https://git.kernel.org/stable/c/1b52aeb40c9f04bf50eeb4ea09142139d163e239","https://git.kernel.org/stable/c/ee8440bb000fff4ef8acbfc99652851e9ca0a35b","https://git.kernel.org/stable/c/547ea9f567498e4accc89e7816264f15a1a0629f","https://git.kernel.org/stable/c/2f55fa28011c97d6495d5787808db10a8c2d690d","https://git.kernel.org/stable/c/e052f920773b73be49eb4d8702a9f85de7464363"],"weaknesses":[],"ingestedAt":"2026-10-30T12:50:04.827Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/80xxx/CVE-2026-80634.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-80634","state":"PUBLISHED","datePublished":"2026-08-28T06:48:49.022Z","dateUpdated":"2026-10-30T12:30:48.907Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-26T14:34:25.777Z"},"containers":{"cna":{"title":"netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag\n\nThe DEV_PATH_BR_VLAN_UNTAG case post-decrements info->num_encaps\ninside WARN_ON_ONCE(). num_encaps is u8, so if it's already 0 the\ndecrement still happens and wraps it to 255. The break only leaves\nthe inner switch -- a later path entry can set info->indev back to\na real device, and we end up returning with num_encaps == 255.\n\nnft_dev_forward_path() then walks info.encap[] (size 2) up to\nnum_encaps, which means an OOB stack read and a bogus count copied\ninto the route descriptor.\n\nShould only happen on a malformed bridge path stack, hence the WARN,\nbut worth handling sanely. Move the decrement out of the WARN.\n\n[ While at this, remove the WARN_ON_ONCE since this can only happen\n  with a buggy bridge path stack --pablo ]."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"9a4e3a9017ba3da2de187b72ed6545641a0d0a84","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"1b52aeb40c9f04bf50eeb4ea09142139d163e239","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"ee8440bb000fff4ef8acbfc99652851e9ca0a35b","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"547ea9f567498e4accc89e7816264f15a1a0629f","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"2f55fa28011c97d6495d5787808db10a8c2d690d","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","status":"affected","lessThan":"e052f920773b73be49eb4d8702a9f85de7464363","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nf_flow_table_path.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.13","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.5","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nf_flow_table_path.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/9a4e3a9017ba3da2de187b72ed6545641a0d0a84"},{"url":"https://git.kernel.org/stable/c/1b52aeb40c9f04bf50eeb4ea09142139d163e239"},{"url":"https://git.kernel.org/stable/c/ee8440bb000fff4ef8acbfc99652851e9ca0a35b"},{"url":"https://git.kernel.org/stable/c/547ea9f567498e4accc89e7816264f15a1a0629f"},{"url":"https://git.kernel.org/stable/c/2f55fa28011c97d6495d5787808db10a8c2d690d"},{"url":"https://git.kernel.org/stable/c/e052f920773b73be49eb4d8702a9f85de7464363"}],"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 hit in nft_flow_offload_eval on NF_INET_FORWARD when remotely sourced TCP/UDP packets matching a conntrack flow trigger nft_flow_route() and nft_dev_forward_path() during softirq packet processing on nftables flowtable routers/gateways, not via netlink configuration APIs.\nAC:L - Once an nftables flowtable with bridge VLAN filtering is deployed, an attacker can establish confirmed TCP/UDP flows and steer traffic through the affected bridge/VLAN topology to reach nft_dev_path_info() without races or other conditions outside the attacker's control.\nPR:N - Flowtable and bridge VLAN setup are administrator deployment prerequisites; a remote sender needs no local account, authentication, or CAP_NET_ADMIN on the victim to trigger flow offload path resolution while forwarding traffic through the configured bridge.\nUI:N - Exploitation requires only sending network packets processed automatically on the forwarding path; no victim must open files, mount filesystems, or take any interactive action beyond normal traffic through the router.\nS:U - Out-of-bounds stack reads and writes in nft_dev_forward_path() corrupt kernel stack memory and route descriptors on the affected host only; this is standard kernel compromise within one security authority, not a VM escape or cross-boundary sandbox break.\nC:H - When num_encaps underflows to 255, nft_dev_forward_path() loops up to 255 times over info.encap[2], performing out-of-bounds stack reads of adjacent kernel stack memory that can disclose pointers and other sensitive data.\nI:H - The same loop writes attacker-influenced encap values past route->tuple[].in.encap[2] on the stack, corrupting adjacent route fields and stack data in ways that can be leveraged for arbitrary kernel writes and control-flow hijack.\nA:H - Massive out-of-bounds stack corruption during flow offload setup in softirq context can cause immediate kernel oops/panic and reliable denial of service on forwarding routers processing malicious traffic through vulnerable bridge VLAN paths."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:30:48.907Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.12.114"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-80634","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T19:19:08.898847Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:26:31.432Z"}}]}}}