Security Advisory—VShell^®, SecureCRT^® and SecureFX^®

It is theoretically possible for an attacker to forge RSA signatures when the RSA key has a public exponent of three.

Posted: January 18, 2007

Description

According to CERT Vulnerability Note VU#845620, "Many RSA implementations may fail to properly verify signatures. Specifically, the verifier may incorrectly parse PKCS-1 padded signatures, ignoring data at the end of a signature. If this data is ignored and a RSA key with a public exponent of three is used, it may be possible to forge the signing key's signature."

VShell, SecureCRT, and SecureFX no longer generate keys with a public exponent of three. VShell has an option that disallows keys with a public exponent of three from being used for authentication. SecureCRT and SecureFX warn before a key with a public exponent of three is used for authentication or accepted from a host.