{"id":"CVE-2026-68170","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-68170","summary":"mptcp: fix stale skb->sk reference on subflow close","details":"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.","published":"2026-08-10T11:59:39.174Z","modified":"2026-08-14T04:04:11.634760767Z","cvss":{"score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"7.1.6"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/625fc6060864889fe3d370cdeffbbab762af3cb4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/bd7aae448f6ee9d82599a4474664de1e6e91a535"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68170.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-68170"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-14T04:04:11.634760767Z"}}