{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-72139", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-08-09T03:40:39.908Z", "datePublished": "2026-08-15T05:53:13.279Z", "dateUpdated": "2026-08-15T05:53:13.279Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-15T05:53:13.279Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: defer md5sig_info kfree past RCU grace period in tcp_connect\n\nThe md5+ao reconciliation in tcp_connect() (net/ipv4/tcp_output.c)\nhas two symmetric branches:\n\n\tif (needs_md5) {\n\t\ttcp_ao_destroy_sock(sk, false);\n\t} else if (needs_ao) {\n\t\ttcp_clear_md5_list(sk);\n\t\tkfree(rcu_replace_pointer(tp->md5sig_info, NULL, ...));\n\t}\n\nBoth branches free a per-socket auth-info object while the socket is\nin TCP_SYN_SENT and is already on the inet ehash (inserted by\ninet_hash_connect() in tcp_v4_connect()). Both branches are reachable\nby softirq RX-path readers that load the corresponding info pointer\nvia implicit RCU before bh_lock_sock_nested() is taken.\n\nThe needs_md5 branch is fixed in the prior patch by re-introducing\nthe call_rcu() free in tcp_ao_destroy_sock(): the equivalent per-key\nloop runs inside tcp_ao_info_free_rcu(), the RCU callback, so by the\ntime it frees each tcp_ao_key all softirq readers that captured the\ncontainer have already completed rcu_read_unlock().\n\nThe needs_ao branch is not symmetric in the same way. The container\nfree can be deferred via kfree_rcu(md5sig, rcu) -- struct\ntcp_md5sig_info already has the required rcu member\n(include/net/tcp.h:1999-2002), and the rest of the tree already does\nthis in the tcp_md5sig_info_add() rollback paths\n(net/ipv4/tcp_ipv4.c:1410, 1436). But the per-key teardown is done\nby tcp_clear_md5_list() in process context BEFORE the container's\nRCU grace period: it walks &md5sig->head and frees each\ntcp_md5sig_key with bare hlist_del + kfree. A concurrent softirq\nreader in __tcp_md5_do_lookup() / __tcp_md5_do_lookup_exact()\n(tcp_ipv4.c:1253, 1298) walks the same list via\nhlist_for_each_entry_rcu() and races with that bare kfree on the\nkeys themselves -- a per-key slab use-after-free of the same class\nas the TCP-AO bug, on the same race window.\n\nFix this in two halves:\n\n 1. Convert the bare kfree() in tcp_connect() to kfree_rcu() so the\n md5sig_info container joins the rest of the md5sig lifecycle.\n The local-variable lift is mechanical and required because\n kfree_rcu() is a macro that expects an lvalue.\n\n 2. Make tcp_clear_md5_list() RCU-safe by replacing hlist_del +\n kfree(key) with hlist_del_rcu + kfree_rcu(key, rcu). struct\n tcp_md5sig_key already carries the rcu member\n (include/net/tcp.h:1995) and tcp_md5_do_del()\n (net/ipv4/tcp_ipv4.c:1456) already uses kfree_rcu, so this\n restores the lifecycle invariant the rest of the file follows\n rather than introducing a one-off.\n\nThe other caller of tcp_clear_md5_list() is tcp_md5_destruct_sock()\n(net/ipv4/tcp.c:412), which runs from the sock destructor when the\nsocket is already unhashed and unreachable; the extra grace period\nthere is unnecessary but harmless. Making the helper unconditionally\nRCU-safe is the cleaner contract.\n\nThe needs_ao branch is not reachable by the userns reproducer used\nto demonstrate the AO-side splat (the repro installs both keys but\nends up in the needs_md5 branch because the connect peer matches\nthe MD5 key, not the AO key); however the symmetric race exists\nand a maintainer touching this code should not have to think about\nwhich branch escapes RCU and which one does not.\n\n[also credits to Qihang, who found that this races with tcp-diag]" } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/ipv4/tcp_ipv4.c", "net/ipv4/tcp_output.c" ], "versions": [ { "version": "51e547e8c89c661f6fbede4a28b1d33b13625683", "lessThan": "33a1bee413628378fd036a4f2b17ba86b0bc560c", "status": "affected", "versionType": "git" }, { "version": "51e547e8c89c661f6fbede4a28b1d33b13625683", "lessThan": "da48b9bf1eb95a9cfd09d615ca58cfc2b03de369", "status": "affected", "versionType": "git" }, { "version": "51e547e8c89c661f6fbede4a28b1d33b13625683", "lessThan": "b74cd55038905d5e74c1de109ab78a30b2ea0e1f", "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/ipv4/tcp_ipv4.c", "net/ipv4/tcp_output.c" ], "versions": [ { "version": "6.18", "status": "affected" }, { "version": "0", "lessThan": "6.18", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.40", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.5", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2-rc2", "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": "6.18", "versionEndExcluding": "6.18.40" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.18", "versionEndExcluding": "7.1.5" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.18", "versionEndExcluding": "7.2-rc2" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/33a1bee413628378fd036a4f2b17ba86b0bc560c" }, { "url": "https://git.kernel.org/stable/c/da48b9bf1eb95a9cfd09d615ca58cfc2b03de369" }, { "url": "https://git.kernel.org/stable/c/b74cd55038905d5e74c1de109ab78a30b2ea0e1f" } ], "title": "tcp: defer md5sig_info kfree past RCU grace period in tcp_connect", "x_generator": { "engine": "bippy-1.2.0" } } } }