CVE-2025-54885

Thinbus Javascript Secure Remote Password is a browser SRP6a implementation for zero-knowledge password authentication. In versions 2.0.0 and below, a protocol compliance bug causes the client to generate a fixed 252 bits of entropy instead of the intended bit length of the safe prime (defaulted to 2048 bits). The client public value is being generated from a private value that is 4 bits below the specification. This reduces the protocol's designed security margin it is now practically exploitable. The servers full sized 2048 bit random number is used to create the shared session key and password proof. This is fixed in version 2.0.1.

Thinbus Javascript Secure Remote Password is a browser SRP6a implementation for zero-knowledge password authentication. In versions 2.0.0 and below, a protocol compliance bug causes the client to generate a fixed 252 bits of entropy instead of the intended bit length of the safe prime (defaulted to 2048 bits). The client public value is being generated from a private value that is 4 bits below the specification. This reduces the protocol's designed security margin it is now practically exploitable. The servers full sized 2048 bit random number is used to create the shared session key and password proof. This is fixed in version 2.0.1.

### Impact A protocol compliance bug in thinbus-srp-npm versions prior to 2.0.1 causes the client to generate a fixed 252 bits of entropy instead of the intended bit length of the safe prime (defaulted to 2048 bits). RFC 5054 states in section [2.5.4 Client Key Exchange ](https://datatracker.ietf.org/doc/html/rfc5054#section-2.5.4) > The client key exchange message carries the client's public value (A). The client calculates this value as A = g^a % N, where a is a random number that SHOULD be at least 256 bits in length. The client public value is being generated from a private value that is 4 bits below the specification. This reduces the protocol's designed security margin it is now practically exploitable. The servers full sized 2048 bit random number is used to create the shared session key and password proof. ### Patches The issue is fixed in versions >= 2.0.1 ### Workarounds It is possible to patch a legacy version: ```javascript // WRONG var hexLength = this.toHex(N).length; // CORRECT var hexLength = this.toHex(this.N()).length; ```

### Impact A protocol compliance bug in thinbus-srp-npm versions prior to 2.0.1 causes the client to generate a fixed 252 bits of entropy instead of the intended bit length of the safe prime (defaulted to 2048 bits). RFC 5054 states in section [2.5.4 Client Key Exchange ](https://datatracker.ietf.org/doc/html/rfc5054#section-2.5.4) > The client key exchange message carries the client's public value (A). The client calculates this value as A = g^a % N, where a is a random number that SHOULD be at least 256 bits in length. The client public value is being generated from a private value that is 4 bits below the specification. This reduces the protocol's designed security margin it is now practically exploitable. The servers full sized 2048 bit random number is used to create the shared session key and password proof. ### Patches The issue is fixed in versions >= 2.0.1 ### Workarounds It is possible to patch a legacy version: ```javascript // WRONG var hexLength = this.toHex(N).length; // CORRECT var hexLength = this.toHex(this.N()).length; ```

Thinbus Javascript Secure Remote Password es una implementación de SRP6a para navegadores que permite la autenticación de contraseñas de conocimiento cero. En las versiones 2.0.0 y anteriores, un error de cumplimiento del protocolo provoca que el cliente genere una entropía fija de 252 bits en lugar de la longitud de bits prevista para el primo seguro (predeterminada en 2048 bits). El valor público del cliente se genera a partir de un valor privado 4 bits por debajo de la especificación. Esto reduce el margen de seguridad diseñado para el protocolo y ahora es prácticamente explotable. El número aleatorio completo de 2048 bits del servidor se utiliza para crear la clave de sesión compartida y la prueba de contraseña. Esto se solucionó en la versión 2.0.1.