{"id":"CVE-2026-68118","state":"PUBLISHED","title":"tcp: challenge ACK for non-exact RST in SYN-RECEIVED","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: challenge ACK for non-exact RST in SYN-RECEIVED\n\nThe SYN-RECEIVED request-socket path in tcp_check_req() accepts an\nin-window RST without requiring SEG.SEQ to exactly match RCV.NXT.  A\nnon-exact RST therefore removes the request instead of eliciting a\nchallenge ACK.\n\nRFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in\nSYN-RECEIVED: an exact RST resets the connection, while a non-exact\nin-window RST must trigger a challenge ACK and be dropped.\n\nApply that check before the ACK-field validation, following the RFC\nsequence-number, RST, then ACK processing order.  Factor the per-netns\nchallenge ACK quota out of tcp_send_challenge_ack() so request sockets\ncan share it.  Use the request socket's send_ack() callback and its own\nout-of-window ACK timestamp to send and rate-limit the response.","publishedAt":"2026-08-10T11:58:38.000Z","updatedAt":"2026-10-30T12:28:06.412Z","severity":{"score":8.2,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"c5dc463cc60eb26079b19607c9dbda76491dad05","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"8b0a3a094f4cae2fb92e4d08d4eef7246a9d9c49","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"0fe4636665d14a258de70b4f3e8248e6d42038f1","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"234f9ffbd9b2c1b24ec67200ea3cff07401bec48","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"22cec809b048495310f206d9abbcdbbfbdce3ae3","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"a28c4fcbf774e23b4779cae468e3497a5ad1f4a1","versionType":"git"},{"version":"86791bbfe5ed7b275be040cfeff049a1624af1b7","status":"affected","versionType":"git"},{"version":"61f69dc4e40e41b0018f00fa4aeb23d3239556fb","status":"affected","versionType":"git"},{"version":"34fb350281ced2a72707a5c0064f69992d440edb","status":"affected","versionType":"git"},{"version":"3.0.58","status":"affected","lessThan":"3.1","versionType":"semver"},{"version":"3.2.37","status":"affected","lessThan":"3.3","versionType":"semver"},{"version":"3.4.25","status":"affected","lessThan":"3.5","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/net/tcp.h","net/ipv4/tcp_input.c","net/ipv4/tcp_minisocks.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.6","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.153","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.105","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.42","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.6","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":["include/net/tcp.h","net/ipv4/tcp_input.c","net/ipv4/tcp_minisocks.c"]}],"references":["https://git.kernel.org/stable/c/c5dc463cc60eb26079b19607c9dbda76491dad05","https://git.kernel.org/stable/c/8b0a3a094f4cae2fb92e4d08d4eef7246a9d9c49","https://git.kernel.org/stable/c/0fe4636665d14a258de70b4f3e8248e6d42038f1","https://git.kernel.org/stable/c/234f9ffbd9b2c1b24ec67200ea3cff07401bec48","https://git.kernel.org/stable/c/22cec809b048495310f206d9abbcdbbfbdce3ae3","https://git.kernel.org/stable/c/a28c4fcbf774e23b4779cae468e3497a5ad1f4a1"],"weaknesses":["CWE-20"],"ingestedAt":"2026-10-30T12:46:06.359Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/68xxx/CVE-2026-68118.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-68118","state":"PUBLISHED","datePublished":"2026-08-10T11:58:38.000Z","dateUpdated":"2026-10-30T12:28:06.412Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-30T09:28:09.369Z"},"containers":{"cna":{"title":"tcp: challenge ACK for non-exact RST in SYN-RECEIVED","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: challenge ACK for non-exact RST in SYN-RECEIVED\n\nThe SYN-RECEIVED request-socket path in tcp_check_req() accepts an\nin-window RST without requiring SEG.SEQ to exactly match RCV.NXT.  A\nnon-exact RST therefore removes the request instead of eliciting a\nchallenge ACK.\n\nRFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in\nSYN-RECEIVED: an exact RST resets the connection, while a non-exact\nin-window RST must trigger a challenge ACK and be dropped.\n\nApply that check before the ACK-field validation, following the RFC\nsequence-number, RST, then ACK processing order.  Factor the per-netns\nchallenge ACK quota out of tcp_send_challenge_ack() so request sockets\ncan share it.  Use the request socket's send_ack() callback and its own\nout-of-window ACK timestamp to send and rate-limit the response."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"c5dc463cc60eb26079b19607c9dbda76491dad05","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"8b0a3a094f4cae2fb92e4d08d4eef7246a9d9c49","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"0fe4636665d14a258de70b4f3e8248e6d42038f1","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"234f9ffbd9b2c1b24ec67200ea3cff07401bec48","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"22cec809b048495310f206d9abbcdbbfbdce3ae3","versionType":"git"},{"version":"282f23c6ee343126156dd41218b22ece96d747e3","status":"affected","lessThan":"a28c4fcbf774e23b4779cae468e3497a5ad1f4a1","versionType":"git"},{"version":"86791bbfe5ed7b275be040cfeff049a1624af1b7","status":"affected","versionType":"git"},{"version":"61f69dc4e40e41b0018f00fa4aeb23d3239556fb","status":"affected","versionType":"git"},{"version":"34fb350281ced2a72707a5c0064f69992d440edb","status":"affected","versionType":"git"},{"version":"3.0.58","status":"affected","lessThan":"3.1","versionType":"semver"},{"version":"3.2.37","status":"affected","lessThan":"3.3","versionType":"semver"},{"version":"3.4.25","status":"affected","lessThan":"3.5","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["include/net/tcp.h","net/ipv4/tcp_input.c","net/ipv4/tcp_minisocks.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.6","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.153","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.105","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.42","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.6","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":["include/net/tcp.h","net/ipv4/tcp_input.c","net/ipv4/tcp_minisocks.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/c5dc463cc60eb26079b19607c9dbda76491dad05"},{"url":"https://git.kernel.org/stable/c/8b0a3a094f4cae2fb92e4d08d4eef7246a9d9c49"},{"url":"https://git.kernel.org/stable/c/0fe4636665d14a258de70b4f3e8248e6d42038f1"},{"url":"https://git.kernel.org/stable/c/234f9ffbd9b2c1b24ec67200ea3cff07401bec48"},{"url":"https://git.kernel.org/stable/c/22cec809b048495310f206d9abbcdbbfbdce3ae3"},{"url":"https://git.kernel.org/stable/c/a28c4fcbf774e23b4779cae468e3497a5ad1f4a1"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H","baseScore":8.2,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - The bug is in tcp_check_req() on the core TCP receive path (ip_rcv/tcp_v4_rcv or tcp_v6_rcv → __inet_lookup_skb on TCP_NEW_SYN_RECV → tcp_check_req); any remote host that can deliver TCP segments to an internet-facing listener reaches it with no local access.\nAC:L - An attacker controls the forged RST (source/dest ports, SEQ sweep across the SYN-RECEIVED window up to tcp_synack_window/65535) and can retry on every handshake; no race, rare config, or victim-only state outside attacker influence is required beyond routine IP spoofing or on-path delivery.\nPR:N - Processing occurs on the pre-authentication TCP handshake path for embryonic request sockets; no credentials, capabilities, or local account are needed—only the ability to send (or spoof) TCP packets to the target listener.\nUI:N - Handshake teardown is triggered automatically when the kernel receives the crafted RST during SYN-RECEIVED; no victim must open files, click links, or perform any other action.\nS:U - Impact is confined to incorrect TCP connection-state handling within the same host kernel; it does not cross VM, container, or IOMMU security boundaries.\nC:N - This is a protocol state-machine logic flaw with no memory corruption, out-of-bounds access, use-after-free, or information disclosure—only embryonic request-socket teardown occurs.\nI:L - A non-exact in-window RST causes unauthorized modification of TCP connection state by dropping the embryonic request socket (embryonic_reset/inet_csk_reqsk_queue_drop) instead of preserving it per RFC 5961/RFC 9293.\nA:H - Repeated spoofed in-window RSTs during SYN-RECEIVED can prevent TCP handshakes from completing on arbitrary listening services (HTTPS, SSH, databases, load balancers), causing sustained denial of service without kernel crash."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:28:06.412Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.6","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.6","versionEndExcluding":"6.6.153"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.6","versionEndExcluding":"6.12.105"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.6","versionEndExcluding":"6.18.42"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.6","versionEndExcluding":"7.1.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.6","versionEndExcluding":"7.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.0.58"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.2.37"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.4.25"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-68118","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T15:44:08.841575Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-20","lang":"en","type":"CWE","description":"CWE-20 Improper Input Validation"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T20:58:51.621Z"}}]}}}