{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-68170", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-30T09:28:09.372Z", "datePublished": "2026-08-10T11:59:39.174Z", "dateUpdated": "2026-08-17T05:00:11.808Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-17T05:00:11.808Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fix stale skb->sk reference on subflow close\n\nThe backlog list is updated by mptcp_data_ready() under\nmptcp_data_lock(). The cleanup of backlog references to a closing\nsubflow, however, was performed in mptcp_close_ssk(), before\n__mptcp_close_ssk() acquires the ssk lock, and while holding neither\nthe ssk lock nor mptcp_data_lock().\n\nBecause that traversal ran without mptcp_data_lock(), concurrent softirq\nRX processing on another CPU (subflow_data_ready() -> mptcp_data_ready()\n-> __mptcp_add_backlog(), under mptcp_data_lock()) could add a backlog\nentry referencing the ssk while the cleanup loop was in progress. Such\nan entry could be missed by the cleanup, or the concurrent list update\ncould corrupt the traversal, leaving skb->sk pointing at the ssk after\nit is freed.\n\nA later mptcp_backlog_purge() then dereferences the stale pointer,\ntriggering a warning in inet_sock_destruct() (ssk->sk_rmem_alloc != 0)\nfollowed by a use-after-free in mptcp_backlog_purge().\n\nFix this by moving the backlog cleanup into __mptcp_close_ssk(), after\nsubflow->closing is set to 1 and while the ssk lock is still held,\nserialized under mptcp_data_lock(). The cleanup runs only on the push\npath (MPTCP_CF_PUSH), where backlog references accumulate; on other\nteardown paths the caller already handles cleanup.\n\nWith subflow->closing set and mptcp_data_lock() held across the purge,\nany concurrent mptcp_data_ready() either completes its enqueue before\nthe purge runs and is caught, or observes closing=1 and bails out. Once\nmptcp_data_unlock() is reached, no new skb referencing the ssk can be\nenqueued, so the cleanup is exhaustive.\n\nRemove the unprotected traversal from mptcp_close_ssk() entirely." } ], "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 in MPTCP receive/teardown on the TCP/IP stack; remote peers drive subflow_data_ready() RX softirq processing and can concurrently trigger subflow close via FIN/RST or data floods during mptcp_close_ssk(), reaching the race without local access.\nAC:L - The attacker controls both sides of the race by timing inbound packets against subflow teardown on an MPTCP connection they own; syzkaller reliably reproduced the UAF, and no uncontrollable memory layout or rare victim state is required beyond an active MPTCP session.\nPR:N - Exploitation needs only the ability to be an MPTCP/TCP peer on the network after handshake; no local account, CAP_NET_ADMIN, or application credentials on the victim are required to send data and close subflows remotely.\nUI:N - No victim user interaction is required beyond the system normally accepting or maintaining MPTCP connections; the attacker can trigger the race entirely through automated network traffic and connection management.\nS:U - The vulnerability corrupts kernel heap memory within the network stack security boundary on the affected host; it does not by itself cross VM, hypervisor, or IOMMU isolation boundaries.\nC:H - A missed backlog cleanup leaves skb->sk pointing at a freed subflow socket; later mptcp_backlog_purge() dereferences it in mptcp_borrow_fwdmem(), producing a slab use-after-free on struct sock that can disclose kernel memory.\nI:H - The UAF performs atomic_sub() writes to sk_rmem_alloc on a freed TCP socket object, corrupting attacker-influenced heap memory and providing a standard path to further arbitrary kernel write or control-flow hijack.\nA:H - Confirmed KASAN slab-use-after-free during mptcp_backlog_purge() causes inet_sock_destruct() warnings and kernel instability during socket teardown; UAF in softirq/close paths can panic or repeatedly crash the host." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/mptcp/protocol.c" ], "versions": [ { "version": "ee458a3f314e9c669ddd227bf5ab08354d9e75cc", "lessThan": "625fc6060864889fe3d370cdeffbbab762af3cb4", "status": "affected", "versionType": "git" }, { "version": "ee458a3f314e9c669ddd227bf5ab08354d9e75cc", "lessThan": "bd7aae448f6ee9d82599a4474664de1e6e91a535", "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/protocol.c" ], "versions": [ { "version": "6.19", "status": "affected" }, { "version": "0", "lessThan": "6.19", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.6", "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": "6.19", "versionEndExcluding": "7.1.6" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "7.2" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/625fc6060864889fe3d370cdeffbbab762af3cb4" }, { "url": "https://git.kernel.org/stable/c/bd7aae448f6ee9d82599a4474664de1e6e91a535" } ], "title": "mptcp: fix stale skb->sk reference on subflow close", "x_generator": { "engine": "bippy-1.2.0" } } } }