{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-80634","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-08-26T14:34:25.777Z","datePublished":"2026-08-28T06:48:49.022Z","dateUpdated":"2026-08-29T06:21:33.944Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-29T06:21:33.944Z"},"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 ]."}],"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."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nf_flow_table_path.c"],"versions":[{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","lessThan":"2f55fa28011c97d6495d5787808db10a8c2d690d","status":"affected","versionType":"git"},{"version":"e990cef6516daa4e1e236433579e333f74fd38cb","lessThan":"e052f920773b73be49eb4d8702a9f85de7464363","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nf_flow_table_path.c"],"versions":[{"version":"5.13","status":"affected"},{"version":"0","lessThan":"5.13","status":"unaffected","versionType":"semver"},{"version":"7.1.5","lessThanOrEqual":"7.1.*","status":"unaffected","versionType":"semver"},{"version":"7.2","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"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"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/2f55fa28011c97d6495d5787808db10a8c2d690d"},{"url":"https://git.kernel.org/stable/c/e052f920773b73be49eb4d8702a9f85de7464363"}],"title":"netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag","x_generator":{"engine":"bippy-1.2.0"}}}}