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CVE-2026-55950

Full vulnerability record from the local CVENow database.

Description

Time-of-check Time-of-use (TOCTOU) race condition vulnerability in Erlang/OTP ssl (dtls_packet_demux module) allows an unauthenticated remote attacker to crash all active DTLS sessions on a listener. A DTLS server listener uses a single shared dtls_packet_demux gen_server process to route incoming UDP datagrams to the correct connection handler. When a DTLS client reconnects rapidly from the same source address and port (sending multiple ClientHello messages in quick succession), a race condition in the demux's internal gb_trees key-value store causes a {key_exists, {old, Client}} crash, terminating the demux process. Because the demux is shared across all DTLS associations on that listener, its crash immediately kills every active DTLS session, not just the attacker's. The attack is pre-authentication: the attacker only needs to send UDP datagrams containing valid ClientHello messages from the same source IP and port before the intermediate DOWN monitor message is processed by the gen_server. No credentials, no completed handshake, and no special configuration are required, and the crash can be repeated indefinitely to create a persistent denial of service for all clients of that listener. This vulnerability is associated with program file lib/ssl/src/dtls_packet_demux.erl. This issue affects OTP from OTP 25.3 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssl from 10.9 before 11.7.3, 11.6.0.3 and 11.2.12.10.

Severity
HIGH
CVSS score
8.7 (v4.0)
Vulnerability status
Modified
Source identifier
6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Published
2026-07-02 17:17:02.910000
Last modified
2026-10-25 21:10:00.770000
View original CVE JSON 
{
  "id": "CVE-2026-55950",
  "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
  "published": "2026-07-02T17:17:02.910",
  "lastModified": "2026-10-25T21:10:00.770",
  "vulnStatus": "Modified",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Time-of-check Time-of-use (TOCTOU) race condition vulnerability in Erlang/OTP ssl (dtls_packet_demux module) allows an unauthenticated remote attacker to crash all active DTLS sessions on a listener.\n\nA DTLS server listener uses a single shared dtls_packet_demux gen_server process to route incoming UDP datagrams to the correct connection handler. When a DTLS client reconnects rapidly from the same source address and port (sending multiple ClientHello messages in quick succession), a race condition in the demux's internal gb_trees key-value store causes a {key_exists, {old, Client}} crash, terminating the demux process. Because the demux is shared across all DTLS associations on that listener, its crash immediately kills every active DTLS session, not just the attacker's.\n\nThe attack is pre-authentication: the attacker only needs to send UDP datagrams containing valid ClientHello messages from the same source IP and port before the intermediate DOWN monitor message is processed by the gen_server. No credentials, no completed handshake, and no special configuration are required, and the crash can be repeated indefinitely to create a persistent denial of service for all clients of that listener.\n\nThis vulnerability is associated with program file lib/ssl/src/dtls_packet_demux.erl.\n\nThis issue affects OTP from OTP 25.3 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssl from 10.9 before 11.7.3, 11.6.0.3 and 11.2.12.10."
    },
    {
      "lang": "es",
      "value": "Vulnerabilidad de condición de carrera Time-of-check Time-of-use (TOCTOU) en Erlang/OTP ssl (módulo dtls_packet_demux) permite a un atacante remoto no autenticado colapsar todas las sesiones DTLS activas en un oyente.\n\nUn oyente de servidor DTLS utiliza un único proceso gen_server dtls_packet_demux compartido para enrutar datagramas UDP entrantes al gestor de conexión correcto. Cuando un cliente DTLS se reconecta rápidamente desde la misma dirección de origen y puerto (enviando múltiples mensajes ClientHello en rápida sucesión), una condición de carrera en el almacén clave-valor gb_trees interno del demux causa un colapso {key_exists, {old, Client}}, terminando el proceso demux. Debido a que el demux se comparte entre todas las asociaciones DTLS en ese oyente, su colapso mata inmediatamente cada sesión DTLS activa, no solo la del atacante.\n\nEl ataque es de pre-autenticación: el atacante solo necesita enviar datagramas UDP que contengan mensajes ClientHello válidos desde la misma IP de origen y puerto antes de que el mensaje de monitor DOWN intermedio sea procesado por el gen_server. No se requieren credenciales, ni un handshake completado, ni una configuración especial, y el colapso puede repetirse indefinidamente para crear una denegación de servicio persistente para todos los clientes de ese oyente.\n\nEsta vulnerabilidad está asociada con el archivo de programa lib/ssl/src/dtls_packet_demux.erl.\n\nEste problema afecta a OTP desde OTP 25.3 antes de 29.0.3, 28.5.0.3 y 27.3.4.14 correspondiente a ssl desde 10.9 antes de 11.7.3, 11.6.0.3 y 11.2.12.10."
    }
  ],
  "affected": [
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      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "affectedData": [
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          "modules": [
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              "name": "dtls_packet_demux:handle_call/3"
            },
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              "name": "dtls_packet_demux:handle_info/2"
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            {
              "name": "dtls_packet_demux:new_connection/2"
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          ],
          "repo": "https://github.com/erlang/otp",
          "packageURL": "pkg:otp/ssl?repository_url=https:%2F%2Fgithub.com%2Ferlang%2Fotp&vcs_url=git%20https:%2F%2Fgithub.com%2Ferlang%2Fotp.git",
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                  "status": "unaffected"
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                  "at": "11.2.12.10",
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              "name": "dtls_packet_demux:handle_info/2"
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            {
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          ],
          "repo": "https://github.com/erlang/otp",
          "packageURL": "pkg:github/erlang/otp",
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              "versionType": "otp",
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                {
                  "at": "28.5.0.3",
                  "status": "unaffected"
                },
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                  "at": "27.3.4.14",
                  "status": "unaffected"
                }
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            },
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              "version": "44dcb4c3d900777493ce2a6129f451aa475811f9",
              "lessThan": "e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04",
              "versionType": "git",
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            }
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        }
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    }
  ],
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          "exploitMaturity": "NOT_DEFINED",
          "confidentialityRequirement": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
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          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
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          "Safety": "NOT_DEFINED",
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "valueDensity": "NOT_DEFINED",
          "vulnerabilityResponseEffort": "NOT_DEFINED",
          "providerUrgency": "NOT_DEFINED"
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    "cvssMetricV31": [
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        "source": "[email protected]",
        "type": "Primary",
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    "ssvcV203": [
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        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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      "description": [
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          "value": "CWE-367"
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      "url": "https://cna.erlef.org/cves/CVE-2026-55950.html",
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}