Problem Description When verifying a PKCS#1 v1.5 signature, OpenSSL ignores any bytes which follow the cryptographic hash being signed. In a valid signature there will be no such bytes. Impact OpenSSL will incorrectly report some invalid signatures as valid. When an RSA public exponent of 3 is used, or more generally when a small public exponent is used with a relatively large modulus (e.g., a public exponent of 17 with a 4096-bit modulus), an attacker can construct a signature which OpenSSL will accept as a valid PKCS#1 v1.5 signature. Workaround No workaround is available.