CVE-2026-54886

Full vulnerability record from the local CVENow database.

Description

Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in Erlang OTP ssh (ssh_sftpd module) allows an authenticated SFTP user to render an SFTP channel permanently unresponsive. The handle_data/4 function in ssh_sftpd contains a catch-all clause that accepts channel data of any type. When channel data with a non-zero type code (SSH_MSG_CHANNEL_EXTENDED_DATA) arrives with an empty pending buffer and a payload at or below the SFTP packet size limit, the clause tail-calls itself with identical arguments, creating an infinite loop. The SFTP protocol operates exclusively on normal channel data (type 0). Extended data (non-zero type) is meaningless for SFTP and is never sent by conforming clients. However, the SSH protocol permits any channel participant to send extended data on an open channel, so an authenticated SFTP client can trigger the loop by sending SSH_MSG_CHANNEL_EXTENDED_DATA with any data_type_code and any non-empty payload at or below the size limit. The targeted ssh_sftpd process enters an infinite tail-recursive loop. It never processes another message, its message queue grows without bound, and it can only be stopped by killing the process. BEAM's reduction-based scheduler preemption continues to function, so other processes on the node are not starved, but each stuck channel process consumes its full CPU time share continuously and accumulates unbounded message queue memory. Opening many channels amplifies the CPU and memory impact. Erlang/OTP SSH configurations using the default max_channels setting (infinity) allow an authenticated user to open unlimited channels per connection, amplifying the attack without requiring multiple TCP connections or authentications. No file contents, credentials, or write access are obtainable through this issue. The impact is limited to denial of service on targeted SFTP channels, with secondary CPU degradation and memory growth. This vulnerability is associated with program file lib/ssh/src/ssh_sftpd.erl and program routine ssh_sftpd:handle_data/4. This issue affects OTP from OTP 17.0 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssh from 3.0.1 before 6.0.2, 5.5.2.2 and 5.2.11.9.

Severity

MEDIUM

CVSS score

5.3 (v4.0)

Vulnerability status

Modified

Source identifier

6b3ad84c-e1a6-4bf7-a703-f496b71e49db

Published

2026-07-02 17:17:02.387000

Last modified

2026-10-25 21:10:00.770000

View original CVE JSON

{
  "id": "CVE-2026-54886",
  "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
  "published": "2026-07-02T17:17:02.387",
  "lastModified": "2026-10-25T21:10:00.770",
  "vulnStatus": "Modified",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in Erlang OTP ssh (ssh_sftpd module) allows an authenticated SFTP user to render an SFTP channel permanently unresponsive.\n\nThe handle_data/4 function in ssh_sftpd contains a catch-all clause that accepts channel data of any type. When channel data with a non-zero type code (SSH_MSG_CHANNEL_EXTENDED_DATA) arrives with an empty pending buffer and a payload at or below the SFTP packet size limit, the clause tail-calls itself with identical arguments, creating an infinite loop.\n\nThe SFTP protocol operates exclusively on normal channel data (type 0). Extended data (non-zero type) is meaningless for SFTP and is never sent by conforming clients. However, the SSH protocol permits any channel participant to send extended data on an open channel, so an authenticated SFTP client can trigger the loop by sending SSH_MSG_CHANNEL_EXTENDED_DATA with any data_type_code and any non-empty payload at or below the size limit.\n\nThe targeted ssh_sftpd process enters an infinite tail-recursive loop. It never processes another message, its message queue grows without bound, and it can only be stopped by killing the process. BEAM's reduction-based scheduler preemption continues to function, so other processes on the node are not starved, but each stuck channel process consumes its full CPU time share continuously and accumulates unbounded message queue memory. Opening many channels amplifies the CPU and memory impact.\n\nErlang/OTP SSH configurations using the default max_channels setting (infinity) allow an authenticated user to open unlimited channels per connection, amplifying the attack without requiring multiple TCP connections or authentications.\n\nNo file contents, credentials, or write access are obtainable through this issue. The impact is limited to denial of service on targeted SFTP channels, with secondary CPU degradation and memory growth.\n\nThis vulnerability is associated with program file lib/ssh/src/ssh_sftpd.erl and program routine ssh_sftpd:handle_data/4.\n\nThis issue affects OTP from OTP 17.0 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssh from 3.0.1 before 6.0.2, 5.5.2.2 and 5.2.11.9."
    },
    {
      "lang": "es",
      "value": "Una vulnerabilidad de bucle con condición de salida inalcanzable (’Bucle Infinito’) en Erlang OTP ssh (módulo ssh_sftpd) permite a un usuario SFTP autenticado dejar un canal SFTP permanentemente sin respuesta.\n\nLa función handle_data/4 en ssh_sftpd contiene una cláusula comodín que acepta datos de canal de cualquier tipo. Cuando los datos de canal con un código de tipo no cero (SSH_MSG_CHANNEL_EXTENDED_DATA) llegan con un búfer pendiente vacío y una carga útil igual o inferior al límite de tamaño del paquete SFTP, la cláusula se llama a sí misma de forma recursiva con argumentos idénticos, creando un bucle infinito.\n\nEl protocolo SFTP opera exclusivamente con datos de canal normales (tipo 0). Los datos extendidos (tipo no cero) no tienen sentido para SFTP y nunca son enviados por clientes conformes. Sin embargo, el protocolo SSH permite a cualquier participante del canal enviar datos extendidos en un canal abierto, por lo que un cliente SFTP autenticado puede activar el bucle enviando SSH_MSG_CHANNEL_EXTENDED_DATA con cualquier data_type_code y cualquier carga útil no vacía igual o inferior al límite de tamaño.\n\nEl proceso ssh_sftpd objetivo entra en un bucle recursivo de cola infinito. Nunca procesa otro mensaje, su cola de mensajes crece sin límite y solo puede detenerse eliminando el proceso. La preferencia del planificador basada en reducción de BEAM sigue funcionando, por lo que otros procesos en el nodo no se quedan sin recursos, pero cada proceso de canal atascado consume continuamente su parte completa de tiempo de CPU y acumula memoria de cola de mensajes ilimitada. Abrir muchos canales amplifica el impacto en la CPU y la memoria.\n\nLas configuraciones de Erlang/OTP SSH que utilizan la configuración predeterminada de max_channels (infinito) permiten a un usuario autenticado abrir canales ilimitados por conexión, amplificando el ataque sin requerir múltiples conexiones TCP o autenticaciones.\n\nNo se pueden obtener contenidos de archivos, credenciales o acceso de escritura a través de este problema. El impacto se limita a la denegación de servicio en los canales SFTP objetivo, con degradación secundaria de la CPU y crecimiento de la memoria.\n\nEsta vulnerabilidad está asociada con el archivo de programa lib/ssh/src/ssh_sftpd.erl y la rutina de programa ssh_sftpd:handle_data/4.\n\nEste problema afecta a OTP desde OTP 17.0 hasta OTP 29.0.3, 28.5.0.3 y 27.3.4.14 correspondiente a ssh desde 3.0.1 hasta 6.0.2, 5.5.2.2 y 5.2.11.9."
    }
  ],
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          "programRoutines": [
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          ],
          "repo": "https://github.com/erlang/otp",
          "packageURL": "pkg:github/erlang/otp",
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    }
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          "exploitMaturity": "NOT_DEFINED",
          "confidentialityRequirement": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
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          "modifiedAttackRequirements": "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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