{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/tcp_ipv4.c",
            "net/ipv4/tcp_output.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "33a1bee413628378fd036a4f2b17ba86b0bc560c",
              "status": "affected",
              "version": "51e547e8c89c661f6fbede4a28b1d33b13625683",
              "versionType": "git"
            },
            {
              "lessThan": "da48b9bf1eb95a9cfd09d615ca58cfc2b03de369",
              "status": "affected",
              "version": "51e547e8c89c661f6fbede4a28b1d33b13625683",
              "versionType": "git"
            },
            {
              "lessThan": "b74cd55038905d5e74c1de109ab78a30b2ea0e1f",
              "status": "affected",
              "version": "51e547e8c89c661f6fbede4a28b1d33b13625683",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/tcp_ipv4.c",
            "net/ipv4/tcp_output.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.18"
            },
            {
              "lessThan": "6.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.40",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.40",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1.5",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "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-\u003emd5sig_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\u0027s\nRCU grace period: it walks \u0026md5sig-\u003ehead 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]"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The UAF is driven by a race between tcp_connect() freeing MD5 keys and softirq RX handlers (tcp_v4_rcv\u2192tcp_inbound_hash\u2192__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\u0027s 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()\u0027d 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."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:40:48.870Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-72139",
    "datePublished": "2026-08-15T05:53:13.279Z",
    "dateReserved": "2026-08-09T03:40:39.908Z",
    "dateUpdated": "2026-08-17T05:40:48.870Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}