161 lines
12 KiB
JSON
161 lines
12 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2026-72139",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2026-08-09T03:40:39.908Z",
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"datePublished": "2026-08-15T05:53:13.279Z",
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"dateUpdated": "2026-08-17T05:40:48.870Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-08-17T05:40:48.870Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"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]"
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 9.8,
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"baseSeverity": "CRITICAL"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:N - The UAF is driven by a race between tcp_connect() freeing MD5 keys and softirq RX handlers (tcp_v4_rcv→tcp_inbound_hash→__tcp_md5_do_lookup) on an ehashed SYN_SENT socket; forged inbound TCP segments reach this path over the network, matching internet-facing BGP/TCP-AO peers.\nAC:L - The attacker controls both sides of the race by calling connect() while concurrently spraying TCP segments (raw sockets or as the remote peer) at the socket 4-tuple; no victim-dependent timing or memory layout is required beyond standard heap reuse inherent to slab UAF.\nPR:N - Exploitation needs no host root: a remote BGP/TCP peer can send segments during the victim's outbound connect, and the demonstrated userns repro uses only uid=1000 with CLONE_NEWUSER|CLONE_NEWNET caps to install TCP_MD5/TCP-AO keys and trigger the race.\nUI:N - No end-user action is required; the bug fires during automated connect() handling (e.g., BGP session establishment) concurrent with inbound packet processing, without anyone opening files or confirming prompts.\nS:U - Impact is confined to kernel memory integrity/availability on the affected host; it does not cross VM, container, or IOMMU security boundaries into another authority.\nC:H - Concurrent hlist_for_each_entry_rcu() over tcp_md5sig_key objects that are being kfree()'d is a slab use-after-free; freed key memory can be reallocated and read during RCU traversal, enabling kernel information disclosure.\nI:H - The per-key UAF corrupts RCU list traversal in softirq and allows attacker-influenced slab reuse, providing a standard path to heap grooming and arbitrary kernel write or control-flow hijack.\nA:H - The symmetric TCP-AO connect race in the same window produces kernel GPF/oops in softirq (KASAN wild-memory-access); this MD5-key UAF in the identical SYN_SENT/ehash race window can panic or hang the system."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"net/ipv4/tcp_ipv4.c",
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"net/ipv4/tcp_output.c"
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],
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"versions": [
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{
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"version": "51e547e8c89c661f6fbede4a28b1d33b13625683",
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"lessThan": "33a1bee413628378fd036a4f2b17ba86b0bc560c",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "51e547e8c89c661f6fbede4a28b1d33b13625683",
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"lessThan": "da48b9bf1eb95a9cfd09d615ca58cfc2b03de369",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "51e547e8c89c661f6fbede4a28b1d33b13625683",
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"lessThan": "b74cd55038905d5e74c1de109ab78a30b2ea0e1f",
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"status": "affected",
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}
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]
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},
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "affected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"net/ipv4/tcp_ipv4.c",
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"net/ipv4/tcp_output.c"
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],
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"versions": [
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{
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"version": "6.18",
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"status": "affected"
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},
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{
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"version": "0",
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"lessThan": "6.18",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.18.40",
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"lessThanOrEqual": "6.18.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.1.5",
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"lessThanOrEqual": "7.1.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.2",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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}
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],
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"cpeApplicability": [
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{
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"nodes": [
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"operator": "OR",
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"negate": false,
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.18",
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"versionEndExcluding": "6.18.40"
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},
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.18",
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.18",
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}
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]
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}
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],
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"references": [
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{
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"url": "https://git.kernel.org/stable/c/33a1bee413628378fd036a4f2b17ba86b0bc560c"
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},
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{
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"url": "https://git.kernel.org/stable/c/da48b9bf1eb95a9cfd09d615ca58cfc2b03de369"
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},
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{
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"url": "https://git.kernel.org/stable/c/b74cd55038905d5e74c1de109ab78a30b2ea0e1f"
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}
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],
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"title": "tcp: defer md5sig_info kfree past RCU grace period in tcp_connect",
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} |