CVE-2026-31669 (GCVE-0-2026-31669)
Vulnerability from cvelistv5
Published
2026-04-24 14:45
Modified
2026-04-27 14:04
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: mptcp: fix slab-use-after-free in __inet_lookup_established The ehash table lookups are lockless and rely on SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability during RCU read-side critical sections. Both tcp_prot and tcpv6_prot have their slab caches created with this flag via proto_register(). However, MPTCP's mptcp_subflow_init() copies tcpv6_prot into tcpv6_prot_override during inet_init() (fs_initcall, level 5), before inet6_init() (module_init/device_initcall, level 6) has called proto_register(&tcpv6_prot). At that point, tcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab remains NULL permanently. This causes MPTCP v6 subflow child sockets to be allocated via kmalloc (falling into kmalloc-4k) instead of the TCPv6 slab cache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so when these sockets are freed without SOCK_RCU_FREE (which is cleared for child sockets by design), the memory can be immediately reused. Concurrent ehash lookups under rcu_read_lock can then access freed memory, triggering a slab-use-after-free in __inet_lookup_established. Fix this by splitting the IPv6-specific initialization out of mptcp_subflow_init() into a new mptcp_subflow_v6_init(), called from mptcp_proto_v6_init() before protocol registration. This ensures tcpv6_prot_override.slab correctly inherits the SLAB_TYPESAFE_BY_RCU slab cache.
References
Impacted products
Vendor Product Version
Linux Linux Version: b19bc2945b40b9fd38e835700907ffe8534ef0de
Version: b19bc2945b40b9fd38e835700907ffe8534ef0de
Version: b19bc2945b40b9fd38e835700907ffe8534ef0de
Version: b19bc2945b40b9fd38e835700907ffe8534ef0de
Version: b19bc2945b40b9fd38e835700907ffe8534ef0de
Version: b19bc2945b40b9fd38e835700907ffe8534ef0de
Version: b19bc2945b40b9fd38e835700907ffe8534ef0de
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{
  "containers": {
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          "programFiles": [
            "net/mptcp/protocol.c",
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      ],
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fix slab-use-after-free in __inet_lookup_established\n\nThe ehash table lookups are lockless and rely on\nSLAB_TYPESAFE_BY_RCU to guarantee socket memory stability\nduring RCU read-side critical sections. Both tcp_prot and\ntcpv6_prot have their slab caches created with this flag\nvia proto_register().\n\nHowever, MPTCP\u0027s mptcp_subflow_init() copies tcpv6_prot into\ntcpv6_prot_override during inet_init() (fs_initcall, level 5),\nbefore inet6_init() (module_init/device_initcall, level 6) has\ncalled proto_register(\u0026tcpv6_prot). At that point,\ntcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab\nremains NULL permanently.\n\nThis causes MPTCP v6 subflow child sockets to be allocated via\nkmalloc (falling into kmalloc-4k) instead of the TCPv6 slab\ncache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so\nwhen these sockets are freed without SOCK_RCU_FREE (which is\ncleared for child sockets by design), the memory can be\nimmediately reused. Concurrent ehash lookups under\nrcu_read_lock can then access freed memory, triggering a\nslab-use-after-free in __inet_lookup_established.\n\nFix this by splitting the IPv6-specific initialization out of\nmptcp_subflow_init() into a new mptcp_subflow_v6_init(), called\nfrom mptcp_proto_v6_init() before protocol registration. This\nensures tcpv6_prot_override.slab correctly inherits the\nSLAB_TYPESAFE_BY_RCU slab cache."
        }
      ],
      "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"
          }
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-27T14:04:53.478Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/f6e1f25fa5e733570f6d6fe37a4dfed2a0deba47"
        },
        {
          "url": "https://git.kernel.org/stable/c/fb1f54b7d16f393b8b65d328410f78b4beea8fcc"
        },
        {
          "url": "https://git.kernel.org/stable/c/3fd6547f5b8ac99687be6d937a0321efda760597"
        },
        {
          "url": "https://git.kernel.org/stable/c/eb9c6aeb512f877cf397deb1e4526f646c70e4a7"
        },
        {
          "url": "https://git.kernel.org/stable/c/15fa9ead4d5e6b6b9c794e84144146c917f2cb62"
        },
        {
          "url": "https://git.kernel.org/stable/c/b313e9037d98c13938740e5ebda7852929366dff"
        },
        {
          "url": "https://git.kernel.org/stable/c/9b55b253907e7431210483519c5ad711a37dafa1"
        }
      ],
      "title": "mptcp: fix slab-use-after-free in __inet_lookup_established",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31669",
    "datePublished": "2026-04-24T14:45:17.295Z",
    "dateReserved": "2026-03-09T15:48:24.130Z",
    "dateUpdated": "2026-04-27T14:04:53.478Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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