{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89554", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.724Z", "datePublished": "2026-09-11T19:44:27.586Z", "dateUpdated": "2026-10-19T08:48:47.068Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:48:47.068Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction\n\nmptcp_token_join_cookie_init_state() restores remote_nonce, local_nonce,\nbackup, join_id, token and msk from the saved cookie entry when rebuilding\nthe request socket for a MP_JOIN 4th-ACK handled under SYN cookies, but it\ndoes not restore local_id, even though the SYN path saved it.\nsubflow_ulp_clone() then reads that uninitialized field and stores it as\nthe joined subflow's address-ID. Because the request-sock slab is\nSLAB_TYPESAFE_BY_RCU and not zeroed on allocation, the value is the stale\nbyte of a previously freed request socket, which an off-path peer can\ninfluence by sending concurrent MP_JOIN SYNs. This corrupts the path\nmanager's id-based subflow bookkeeping for the connection.\n\nRestore subflow_req->local_id from the cookie entry, as done for the other\nfields." } ], "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 flaw is on the MPTCP MP_JOIN SYN-cookie receive path (tcp_v4_rcv/cookie_v4_check/mptcp_subflow_init_cookie_req/mptcp_token_join_cookie_init_state then subflow_ulp_clone). Any remote peer that can reach an MPTCP listener over routed IP triggers it with MP_JOIN packets when SYN cookies are in use.\nAC:L - An attacker can fill the SYN queue to force cookies (tcp_syncookies defaults to 1), spray concurrent MP_JOIN SYNs to seed the SLAB_TYPESAFE_BY_RCU request-sock cache with chosen local_id values, then complete a cookie MP_JOIN ACK. The attacker drives both the flood and the handshake; success does not depend on uninfluencable victim state.\nPR:N - No local account or capability is required. Any unauthenticated remote client obtains a token by completing MP_CAPABLE to a public MPTCP listener, then drives cookie JOIN; HMAC-valid JOIN from that peer, or slab poisoning of another connection's JOIN, needs no victim credentials.\nUI:N - Cookie MP_JOIN reconstruction runs in TCP receive softirq on attacker-sent segments; no local user mount, click, or other action is required beyond ordinary network reachability of an MPTCP service.\nS:U - Impact is confined to the host kernel's MPTCP path-manager and connection state and does not cross a VM, IOMMU, container, or other security authority.\nC:N - The uninitialized field is a single u8 address-ID leftover from a same-type request-sock slab object. It is not an out-of-bounds or pointer leak and does not disclose kernel memory contents to the attacker.\nI:L - subflow_ulp_clone stores the stale local_id as the joined subflow's address-ID, corrupting path-manager id-based bookkeeping (endpoint availability, ADD_ADDR/REMOVE_ADDR matching, and ID-0 primary-path identity). The modification is limited to that protocol ID and is not an arbitrary kernel write or control-flow primitive.\nA:H - A poisoned local_id of 0 or a colliding endpoint ID makes later REMOVE_ADDR/RMSUBFLOW close the initial or other still-needed subflows via mptcp_close_ssk, and desynchronized PM state can reject further joins or tear down the MPTCP session. An attacker can repeat this against many connections on an internet-facing MPTCP service." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/mptcp/syncookies.c" ], "versions": [ { "version": "9466a1ccebbe54ac57fb8a89c2b4b854826546a8", "lessThan": "4534e0eead692bb069ad1e6a5a245fc2e2078300", "status": "affected", "versionType": "git" }, { "version": "9466a1ccebbe54ac57fb8a89c2b4b854826546a8", "lessThan": "63cacb05e51a1c6e1349d2e593d00fd6ef43def4", "status": "affected", "versionType": "git" }, { "version": "9466a1ccebbe54ac57fb8a89c2b4b854826546a8", "lessThan": "954b5ea836eb118d188975ced803448537ab8479", "status": "affected", "versionType": "git" }, { "version": "9466a1ccebbe54ac57fb8a89c2b4b854826546a8", "lessThan": "9df36a4846375a9b75bf42d77bfed216b0f366f9", "status": "affected", "versionType": "git" }, { "version": "9466a1ccebbe54ac57fb8a89c2b4b854826546a8", "lessThan": "64f2c5dd49b956a542c8c02b8dad5d262a462bba", "status": "affected", "versionType": "git" }, { "version": "9466a1ccebbe54ac57fb8a89c2b4b854826546a8", "lessThan": "51887ccd88791ddaa8755a7c614fda031ecf7982", "status": "affected", "versionType": "git" }, { "version": "9466a1ccebbe54ac57fb8a89c2b4b854826546a8", "lessThan": "bf19d166337c6488b39cb03eeeffb30a941d6326", "status": "affected", "versionType": "git" }, { "version": "9466a1ccebbe54ac57fb8a89c2b4b854826546a8", "lessThan": "b878dfdd12d7a5b8722a78d35e313506140ca3d9", "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/mptcp/syncookies.c" ], "versions": [ { "version": "5.9", "status": "affected" }, { "version": "0", "lessThan": "5.9", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.270", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.221", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.188", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.157", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.109", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.50", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.4", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "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": "5.9", "versionEndExcluding": "5.10.270" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.9", "versionEndExcluding": "5.15.221" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.9", "versionEndExcluding": "6.1.188" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.9", "versionEndExcluding": "6.6.157" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.9", "versionEndExcluding": "6.12.109" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.9", "versionEndExcluding": "6.18.50" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.9", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.9", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/4534e0eead692bb069ad1e6a5a245fc2e2078300" }, { "url": "https://git.kernel.org/stable/c/63cacb05e51a1c6e1349d2e593d00fd6ef43def4" }, { "url": "https://git.kernel.org/stable/c/954b5ea836eb118d188975ced803448537ab8479" }, { "url": "https://git.kernel.org/stable/c/9df36a4846375a9b75bf42d77bfed216b0f366f9" }, { "url": "https://git.kernel.org/stable/c/64f2c5dd49b956a542c8c02b8dad5d262a462bba" }, { "url": "https://git.kernel.org/stable/c/51887ccd88791ddaa8755a7c614fda031ecf7982" }, { "url": "https://git.kernel.org/stable/c/bf19d166337c6488b39cb03eeeffb30a941d6326" }, { "url": "https://git.kernel.org/stable/c/b878dfdd12d7a5b8722a78d35e313506140ca3d9" } ], "title": "mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2026-89554", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "yes" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2026-10-16T19:23:57.686804Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-16T19:26:43.610Z" } } ] } }