{"id":"CVE-2026-72418","state":"PUBLISHED","title":"netfilter: nf_conncount: prevent connlimit drops for early confirmed ct","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nf_conncount: prevent connlimit drops for early confirmed ct\n\nCommit 69894e5b4c5e (\"netfilter: nft_connlimit: update the count if add\nwas skipped\") introduced a regression where packets for valid\nconnections are dropped when using connlimit for soft-limiting\nscenarios.\n\nThe issue occurs when a new connection reuses a socket currently in\nthe TIME_WAIT state. In this scenario, the connection tracking entry\nis evaluated as already confirmed. Previously, __nf_conncount_add()\nassumed that if a connection was confirmed and did not originate from\nthe loopback interface, it should skip the addition and return -EEXIST.\n\nSkipping the addition triggers a garbage collection run that cleans up\nthe TIME_WAIT connection. Consequently, the active connection count\ndrops to 0, which xt_connlimit mishandles, leading to the false rejection\nof the perfectly valid new connection.\n\nFix this by replacing the interface check with protocol-agnostic state\nchecks. We now skip the tree insertion and preserve the lockless garbage\ncollection optimization only if the connection is IPS_ASSURED. This\nallows early-confirmed setup packets (such as reused TIME_WAIT sockets\nor locally generated SYN-ACKs) to be properly evaluated and counted\nwithout falsely dropping. The goto check_connections path is maintained\nto ensure these setup packets are deduplicated correctly.\n\nThis has been tested with slowhttptest and HTTP server configured\nlocally to ensure we are not breaking soft-limiting scenarios for local\nor external connections. In addition, it was tested with a OVS zone\nlimit too.","publishedAt":"2026-08-15T05:56:38.374Z","updatedAt":"2026-10-16T18:55:22.660Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"460c112e1d887b58b06b56e8e0230058906ff2c3","status":"affected","lessThan":"000ac6830b56499d6b65fd91486ce6689eb02be4","versionType":"git"},{"version":"53bc0ac47f4f7621c991807bc90e01df49561ac8","status":"affected","lessThan":"cbe2d14a7c5b1fc71821fbfee5c4963917411e92","versionType":"git"},{"version":"ca8b4d1d6304a84ce2016fa2fe9a114b9607b839","status":"affected","lessThan":"3793d24de224943e0a6016bbeffb6f5c4cea2e3d","versionType":"git"},{"version":"8286c02fe9100330475331253fc590f047963f90","status":"affected","lessThan":"abef7f817217fcb62c11821d6b895063eadb2828","versionType":"git"},{"version":"b29ddccf36946a90323486221f39e9f88cc01b8e","status":"affected","lessThan":"ebfe8249ba79e4ff0f1e3aad8787b992ef27f026","versionType":"git"},{"version":"77ea3d8ac3d3d59b5ac9ad639e4ba107c0f2ff1e","status":"affected","lessThan":"329f2626ee5cb8fafdf6b58b624311529c57cb45","versionType":"git"},{"version":"69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e","status":"affected","lessThan":"be52572c6d55f677ba76869d3c63805c0d4891a3","versionType":"git"},{"version":"69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e","status":"affected","lessThan":"c8b6f36f766991e3ebebec6596daee4b04dcbc49","versionType":"git"},{"version":"f85623af16b83615e5f64a9b19ae1d584805cb07","status":"affected","versionType":"git"},{"version":"5.10.248","status":"affected","lessThan":"5.10.261","versionType":"semver"},{"version":"5.15.198","status":"affected","lessThan":"5.15.212","versionType":"semver"},{"version":"6.1.160","status":"affected","lessThan":"6.1.178","versionType":"semver"},{"version":"6.6.120","status":"affected","lessThan":"6.6.145","versionType":"semver"},{"version":"6.12.63","status":"affected","lessThan":"6.12.97","versionType":"semver"},{"version":"6.18.2","status":"affected","lessThan":"6.18.40","versionType":"semver"},{"version":"6.17.13","status":"affected","lessThan":"6.18","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nf_conncount.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.19","versionType":"semver"},{"version":"5.10.261","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.212","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","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_conncount.c"]}],"references":["https://git.kernel.org/stable/c/000ac6830b56499d6b65fd91486ce6689eb02be4","https://git.kernel.org/stable/c/cbe2d14a7c5b1fc71821fbfee5c4963917411e92","https://git.kernel.org/stable/c/3793d24de224943e0a6016bbeffb6f5c4cea2e3d","https://git.kernel.org/stable/c/abef7f817217fcb62c11821d6b895063eadb2828","https://git.kernel.org/stable/c/ebfe8249ba79e4ff0f1e3aad8787b992ef27f026","https://git.kernel.org/stable/c/329f2626ee5cb8fafdf6b58b624311529c57cb45","https://git.kernel.org/stable/c/be52572c6d55f677ba76869d3c63805c0d4891a3","https://git.kernel.org/stable/c/c8b6f36f766991e3ebebec6596daee4b04dcbc49"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/72xxx/CVE-2026-72418.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-72418","state":"PUBLISHED","datePublished":"2026-08-15T05:56:38.374Z","dateUpdated":"2026-10-16T18:55:22.660Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-09T03:40:39.927Z"},"containers":{"cna":{"title":"netfilter: nf_conncount: prevent connlimit drops for early confirmed ct","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nf_conncount: prevent connlimit drops for early confirmed ct\n\nCommit 69894e5b4c5e (\"netfilter: nft_connlimit: update the count if add\nwas skipped\") introduced a regression where packets for valid\nconnections are dropped when using connlimit for soft-limiting\nscenarios.\n\nThe issue occurs when a new connection reuses a socket currently in\nthe TIME_WAIT state. In this scenario, the connection tracking entry\nis evaluated as already confirmed. Previously, __nf_conncount_add()\nassumed that if a connection was confirmed and did not originate from\nthe loopback interface, it should skip the addition and return -EEXIST.\n\nSkipping the addition triggers a garbage collection run that cleans up\nthe TIME_WAIT connection. Consequently, the active connection count\ndrops to 0, which xt_connlimit mishandles, leading to the false rejection\nof the perfectly valid new connection.\n\nFix this by replacing the interface check with protocol-agnostic state\nchecks. We now skip the tree insertion and preserve the lockless garbage\ncollection optimization only if the connection is IPS_ASSURED. This\nallows early-confirmed setup packets (such as reused TIME_WAIT sockets\nor locally generated SYN-ACKs) to be properly evaluated and counted\nwithout falsely dropping. The goto check_connections path is maintained\nto ensure these setup packets are deduplicated correctly.\n\nThis has been tested with slowhttptest and HTTP server configured\nlocally to ensure we are not breaking soft-limiting scenarios for local\nor external connections. In addition, it was tested with a OVS zone\nlimit too."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"460c112e1d887b58b06b56e8e0230058906ff2c3","status":"affected","lessThan":"000ac6830b56499d6b65fd91486ce6689eb02be4","versionType":"git"},{"version":"53bc0ac47f4f7621c991807bc90e01df49561ac8","status":"affected","lessThan":"cbe2d14a7c5b1fc71821fbfee5c4963917411e92","versionType":"git"},{"version":"ca8b4d1d6304a84ce2016fa2fe9a114b9607b839","status":"affected","lessThan":"3793d24de224943e0a6016bbeffb6f5c4cea2e3d","versionType":"git"},{"version":"8286c02fe9100330475331253fc590f047963f90","status":"affected","lessThan":"abef7f817217fcb62c11821d6b895063eadb2828","versionType":"git"},{"version":"b29ddccf36946a90323486221f39e9f88cc01b8e","status":"affected","lessThan":"ebfe8249ba79e4ff0f1e3aad8787b992ef27f026","versionType":"git"},{"version":"77ea3d8ac3d3d59b5ac9ad639e4ba107c0f2ff1e","status":"affected","lessThan":"329f2626ee5cb8fafdf6b58b624311529c57cb45","versionType":"git"},{"version":"69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e","status":"affected","lessThan":"be52572c6d55f677ba76869d3c63805c0d4891a3","versionType":"git"},{"version":"69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e","status":"affected","lessThan":"c8b6f36f766991e3ebebec6596daee4b04dcbc49","versionType":"git"},{"version":"f85623af16b83615e5f64a9b19ae1d584805cb07","status":"affected","versionType":"git"},{"version":"5.10.248","status":"affected","lessThan":"5.10.261","versionType":"semver"},{"version":"5.15.198","status":"affected","lessThan":"5.15.212","versionType":"semver"},{"version":"6.1.160","status":"affected","lessThan":"6.1.178","versionType":"semver"},{"version":"6.6.120","status":"affected","lessThan":"6.6.145","versionType":"semver"},{"version":"6.12.63","status":"affected","lessThan":"6.12.97","versionType":"semver"},{"version":"6.18.2","status":"affected","lessThan":"6.18.40","versionType":"semver"},{"version":"6.17.13","status":"affected","lessThan":"6.18","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/netfilter/nf_conncount.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.19","versionType":"semver"},{"version":"5.10.261","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.212","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.178","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.145","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.97","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.40","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_conncount.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/000ac6830b56499d6b65fd91486ce6689eb02be4"},{"url":"https://git.kernel.org/stable/c/cbe2d14a7c5b1fc71821fbfee5c4963917411e92"},{"url":"https://git.kernel.org/stable/c/3793d24de224943e0a6016bbeffb6f5c4cea2e3d"},{"url":"https://git.kernel.org/stable/c/abef7f817217fcb62c11821d6b895063eadb2828"},{"url":"https://git.kernel.org/stable/c/ebfe8249ba79e4ff0f1e3aad8787b992ef27f026"},{"url":"https://git.kernel.org/stable/c/329f2626ee5cb8fafdf6b58b624311529c57cb45"},{"url":"https://git.kernel.org/stable/c/be52572c6d55f677ba76869d3c63805c0d4891a3"},{"url":"https://git.kernel.org/stable/c/c8b6f36f766991e3ebebec6596daee4b04dcbc49"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - Exploitation is triggered by remote TCP packets processed through netfilter INPUT/FORWARD hooks (xt_connlimit, nft_connlimit, OVS ct-limit) that call nf_conncount_count_skb() on received skbs; no local syscall or ioctl is required.\nAC:L - An unauthenticated remote attacker can reliably trigger the bug by rapidly reconnecting to reuse a TIME_WAIT 4-tuple, a normal TCP behavior they fully control; no race against unrelated system events is required.\nPR:N - The attacker needs no privileges on the victim host; only inbound network access to a service protected by admin-configured connlimit rules is required, and no CAP_NET_ADMIN or namespace capabilities are needed to trigger the faulty counting path.\nUI:N - No victim user action is required; exploitation is achieved solely by sending crafted connection patterns over the network to a host already running connlimit enforcement.\nS:U - Impact is confined to incorrect netfilter connection accounting and packet drops within the same kernel/network security domain; there is no cross-boundary escape such as VM breakout or privilege escalation.\nC:N - The flaw is a connection-count bookkeeping error and premature garbage collection; it does not read kernel memory, leak data, or involve any memory corruption primitive.\nI:N - No unauthorized modification of data or code occurs; the only effect is dropping or mis-evaluating packets against connlimit policy, which is an availability concern rather than integrity compromise.\nA:H - When the miscount drives the connection count to zero, xt_connlimit hot-drops valid packets, falsely rejecting legitimate new connections and causing repeatable denial of service against protected services without authentication."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-17T05:43:58.352Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.10.248","versionEndExcluding":"5.10.261"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15.198","versionEndExcluding":"5.15.212"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.1.160","versionEndExcluding":"6.1.178"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6.120","versionEndExcluding":"6.6.145"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12.63","versionEndExcluding":"6.12.97"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18.2","versionEndExcluding":"6.18.40"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19","versionEndExcluding":"7.1.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19","versionEndExcluding":"7.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.17.13"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-72418","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T18:49:23.434729Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T18:55:22.660Z"}}]}}}