{
  "cveId": "CVE-2026-72139",
  "url": "https://patchblox.com/security/cve/CVE-2026-72139",
  "summary": "CVE-2026-72139 is fixed in 20 products on 1 platform, first by DEBIAN-CVE-2026-72139, released August 15, 2026. It is not reported as exploited. Patch Radar priority: Urgent.",
  "title": "linux: In the Linux kernel, the following vulnerability has been resolved:  tcp: defer md5sig_info kfree past RCU grace peri...",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  tcp: defer md5sig_info kfree past RCU grace period in tcp_connect  The md5\u002Bao reconciliation in tcp_connect() (net/ipv4/tcp_output.c) has two symmetric branches:  \tif (needs_md5) { \t\ttcp_ao_destroy_sock(sk, false); \t} else if (needs_ao) { \t\ttcp_clear_md5_list(sk); \t\tkfree(rcu_replace_pointer(tp-\u003Emd5sig_info, NULL, ...)); \t}  Both branches free a per-socket auth-info object while the socket is in TCP_SYN_SENT and is already on the inet ehash (inserted by inet_hash_connect() in tcp_v4_connect()). Both branches are reachable by softirq RX-path readers that load the corresponding info pointer via implicit RCU before bh_lock_sock_nested() is taken.  The needs_md5 branch is fixed in the prior patch by re-introducing the call_rcu() free in tcp_ao_destroy_sock(): the equivalent per-key loop runs inside tcp_ao_info_free_rcu(), the RCU callback, so by the time it frees each tcp_ao_key all softirq readers that captured the container have already completed rcu_read_unlock().  The needs_ao branch is not symmetric in the same way. The container free can be deferred via kfree_rcu(md5sig, rcu) -- struct tcp_md5sig_info already has the required rcu member (include/net/tcp.h:1999-2002), and the rest of the tree already does this in the tcp_md5sig_info_add() rollback paths (net/ipv4/tcp_ipv4.c:1410, 1436). But the per-key teardown is done by tcp_clear_md5_list() in process context BEFORE the container\u0027s RCU grace period: it walks \u0026md5sig-\u003Ehead and frees each tcp_md5sig_key with bare hlist_del \u002B kfree. A concurrent softirq reader in __tcp_md5_do_lookup() / __tcp_md5_do_lookup_exact() (tcp_ipv4.c:1253, 1298) walks the same list via hlist_for_each_entry_rcu() and races with that bare kfree on the keys themselves -- a per-key slab use-after-free of the same class as the TCP-AO bug, on the same race window.  Fix this in two halves:    1. Convert the bare kfree() in tcp_connect() to kfree_rcu() so the      md5sig_info container joins the rest of the md5sig lifecycle.      The local-variable lift is mechanical and required because      kfree_rcu() is a macro that expects an lvalue.    2. Make tcp_clear_md5_list() RCU-safe by replacing hlist_del \u002B      kfree(key) with hlist_del_rcu \u002B kfree_rcu(key, rcu). struct      tcp_md5sig_key already carries the rcu member      (include/net/tcp.h:1995) and tcp_md5_do_del()      (net/ipv4/tcp_ipv4.c:1456) already uses kfree_rcu, so this      restores the lifecycle invariant the rest of the file follows      rather than introducing a one-off.  The other caller of tcp_clear_md5_list() is tcp_md5_destruct_sock() (net/ipv4/tcp.c:412), which runs from the sock destructor when the socket is already unhashed and unreachable; the extra grace period there is unnecessary but harmless. Making the helper unconditionally RCU-safe is the cleaner contract.  The needs_ao branch is not reachable by the userns reproducer used to demonstrate the AO-side splat (the repro installs both keys but ends up in the needs_md5 branch because the connect peer matches the MD5 key, not the AO key); however the symmetric race exists and a maintainer touching this code should not have to think about which branch escapes RCU and which one does not.  [also credits to Qihang, who found that this races with tcp-diag]",
  "published": "2026-08-15T06:21:31Z",
  "severity": "critical",
  "cvss": 9.8,
  "cvssVector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
  "epss": 0.00631,
  "epssPercentile": 0.50532,
  "priority": "Urgent",
  "priorityTier": 2,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "bpftool6.18",
      "release": "amzn 2023",
      "fixedVersion": "1:6.18.41-94.142.amzn2023",
      "fix": "ALAS2023-2026-2071",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-2071",
      "released": "2026-08-31T09:00:00Z"
    },
    {
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      "release": "amzn 2023",
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      "fix": "ALAS2023-2026-2071",
      "url": "https://patchblox.com/security/fix/linux/alas2023-2026-2071",
      "released": "2026-08-31T09:00:00Z"
    },
    {
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      "fix": "ALAS2023-2026-2071",
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      "released": "2026-08-31T09:00:00Z"
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      "released": "2026-08-31T09:00:00Z"
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    },
    {
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      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-72139",
      "released": "2026-08-15T22:38:55Z"
    },
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  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-09T01:18:40Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}