CVE-2026-98432 (GCVE-0-2026-98432)
Vulnerability from cvelistv5
Published
2026-10-15 12:08
Modified
2026-10-24 14:08
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: ipv4: free inet_opt and ireq_opt after an RCU grace period tcp_v4_syn_recv_sock() transfers ownership of ireq->ireq_opt to the child socket (newinet->inet_opt) without copying it. Another cpu can concurrently process a retransmitted SYN for the same request socket, and send a SYNACK from tcp_check_req(). tcp_v4_send_synack() and inet_csk_route_req() read ireq->ireq_opt under rcu_read_lock() only, and ip_build_and_send_pkt() and ip_options_build() then read opt->optlen twice. Note that the SYNACK timer itself is not an issue: it holds a reference on its request socket, and inet_csk_reqsk_queue_drop() calls timer_delete_sync() before the child can be freed. Since commit 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table"), request sockets are processed without holding the listener lock, so nothing prevents the child socket from being freed while the SYNACK is still being built. TCP child sockets do not have SOCK_RCU_FREE, and inet_sock_destruct() frees inet_opt with a plain kfree(), leading to a use-after-free in ip_options_build(). A similar issue exists with request socket migration (net.ipv4.tcp_migrate_req=1, or a BPF_SK_REUSEPORT_SELECT_OR_MIGRATE program). reqsk_timer_handler() clones the request socket with inet_reqsk_clone(), so that the old request socket and its clone share the same ireq_opt, then reqsk_migrate_reset() clears the pointer in the old one. Another cpu holding a reference on the old request socket can still be using these options (sending a SYNACK, or creating a child in tcp_v4_syn_recv_sock()) when the clone is freed, and tcp_v4_reqsk_destructor() also uses a plain kfree(). Readers already use RCU, and other paths replacing inet_opt (do_ip_setsockopt(), cipso_v4_sock_setattr()...) already use kfree_rcu(). Use kfree_rcu() in inet_sock_destruct() and tcp_v4_reqsk_destructor() as well. IPv6 is not affected by the first issue, because tcp_v6_syn_recv_sock() duplicates the options. tcp_v6_reqsk_destructor() has the same migration issue with ipv6_opt, which is only set by CALIPSO. This will be addressed in a separate patch.
References
Impacted products
Vendor Product Version
Linux Linux Version: 079096f103faca2dd87342cca6f23d4b34da8871
Version: 079096f103faca2dd87342cca6f23d4b34da8871
Version: 079096f103faca2dd87342cca6f23d4b34da8871
Version: 079096f103faca2dd87342cca6f23d4b34da8871
Version: 079096f103faca2dd87342cca6f23d4b34da8871
Version: 079096f103faca2dd87342cca6f23d4b34da8871
Version: 079096f103faca2dd87342cca6f23d4b34da8871
Version: 079096f103faca2dd87342cca6f23d4b34da8871
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/af_inet.c",
            "net/ipv4/tcp_ipv4.c"
          ],
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          "vendor": "Linux",
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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            },
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              "version": "0",
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              "version": "5.10.272",
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            {
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              "lessThanOrEqual": "6.1.*",
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              "lessThanOrEqual": "6.6.*",
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              "version": "7.2.10",
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            },
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: free inet_opt and ireq_opt after an RCU grace period\n\ntcp_v4_syn_recv_sock() transfers ownership of ireq-\u003eireq_opt to the\nchild socket (newinet-\u003einet_opt) without copying it.\n\nAnother cpu can concurrently process a retransmitted SYN for the same\nrequest socket, and send a SYNACK from tcp_check_req().\ntcp_v4_send_synack() and inet_csk_route_req() read ireq-\u003eireq_opt\nunder rcu_read_lock() only, and ip_build_and_send_pkt() and\nip_options_build() then read opt-\u003eoptlen twice.\n\nNote that the SYNACK timer itself is not an issue: it holds a\nreference on its request socket, and inet_csk_reqsk_queue_drop()\ncalls timer_delete_sync() before the child can be freed.\n\nSince commit 079096f103fa (\"tcp/dccp: install syn_recv requests\ninto ehash table\"), request sockets are processed without holding\nthe listener lock, so nothing prevents the child socket from being\nfreed while the SYNACK is still being built. TCP child sockets do\nnot have SOCK_RCU_FREE, and inet_sock_destruct() frees inet_opt\nwith a plain kfree(), leading to a use-after-free in\nip_options_build().\n\nA similar issue exists with request socket migration\n(net.ipv4.tcp_migrate_req=1, or a BPF_SK_REUSEPORT_SELECT_OR_MIGRATE\nprogram). reqsk_timer_handler() clones the request socket with\ninet_reqsk_clone(), so that the old request socket and its clone\nshare the same ireq_opt, then reqsk_migrate_reset() clears the\npointer in the old one. Another cpu holding a reference on the old\nrequest socket can still be using these options (sending a SYNACK,\nor creating a child in tcp_v4_syn_recv_sock()) when the clone is\nfreed, and tcp_v4_reqsk_destructor() also uses a plain kfree().\n\nReaders already use RCU, and other paths replacing inet_opt\n(do_ip_setsockopt(), cipso_v4_sock_setattr()...) already use\nkfree_rcu(). Use kfree_rcu() in inet_sock_destruct() and\ntcp_v4_reqsk_destructor() as well.\n\nIPv6 is not affected by the first issue, because tcp_v6_syn_recv_sock()\nduplicates the options. tcp_v6_reqsk_destructor() has the same\nmigration issue with ipv6_opt, which is only set by CALIPSO. This\nwill be addressed in a separate patch."
        }
      ],
      "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 - An unauthenticated peer supplies IPv4 Record Route or Timestamp bytes in a TCP SYN; ip_rcv_options() and tcp_v4_save_options() store them in ireq_opt. Its retransmitted SYN follows tcp_v4_rcv()-\u003etcp_check_req()-\u003etcp_rtx_synack()-\u003etcp_v4_send_synack(), racing frees in patched inet_sock_destruct() or tcp_v4_reqsk_destructor().\nAC:L - On an accepting server, the peer can repeatedly create an option-bearing request and race a retransmitted SYN against completing and tearing down that same TCP connection. Both racing sides are attacker-induced; multicore scheduling and heap grooming do not constitute conditions outside the attacker\u0027s influence.\nPR:N - tcp_v4_rcv() reaches tcp_check_req() and tcp_v4_send_synack() during the TCP handshake, before application authentication. The target performs no capability or credential check on the peer\u0027s valid IPv4 Record Route or Timestamp option.\nUI:N - The peer sends the option-bearing SYN, retransmitted SYN, and handshake or teardown packets to an already listening service; no victim user must mount, open, or approve anything.\nS:U - The stale ip_options_rcu object is consumed and corrupts memory within the same host kernel in ip_build_and_send_pkt() and ip_options_build(); no separate security authority is crossed.\nC:H - After inet_sock_destruct() frees inet_opt, ip_options_build() copies opt-\u003e__data for the stale opt-\u003eoptlen into the network-bound SYNACK. Reclaiming the object can therefore disclose adjacent kernel heap contents directly to the peer.\nI:H - Reclaiming the freed ip_options_rcu lets stale optlen and srr, rr, or ts offsets steer ip_options_build() memcpy and address or timestamp writes, permitting out-of-bounds kernel writes and potential control-flow corruption.\nA:H - A reclaimed optlen can make ip_build_and_send_pkt() call skb_push() beyond the SYNACK headroom, invoking skb_under_panic(); the stale-offset writes in ip_options_build() can also oops the kernel."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-24T14:08:46.326Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/b3b027ef0cd322bfa839b9aaf5b27551eea54cf6"
        },
        {
          "url": "https://git.kernel.org/stable/c/95a8c8fa9f27dce64c40c41c062de7728bf34ab5"
        },
        {
          "url": "https://git.kernel.org/stable/c/89b5b1eb7d633c33832b7ff2c02e19a144705036"
        },
        {
          "url": "https://git.kernel.org/stable/c/742f73df544e03744f2981c467d6542fe8172a2a"
        },
        {
          "url": "https://git.kernel.org/stable/c/11a03ce3c4a62d84c10ccdfe47f8075006498568"
        },
        {
          "url": "https://git.kernel.org/stable/c/a47406c769f72c070386985488f1c4d057df86b2"
        },
        {
          "url": "https://git.kernel.org/stable/c/26d4c36d318cffbbd160884a0e4cec0da4da4936"
        },
        {
          "url": "https://git.kernel.org/stable/c/e3f33b0a1d89d738e2b913dab519226eaf76e15b"
        }
      ],
      "title": "ipv4: free inet_opt and ireq_opt after an RCU grace period",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98432",
    "datePublished": "2026-10-15T12:08:22.205Z",
    "dateReserved": "2026-09-25T10:25:14.348Z",
    "dateUpdated": "2026-10-24T14:08:46.326Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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