Security: OpenSSL Vulnerable to Forged Signatures

Posted by Vivek Gite [Last updated: September 10, 2006]

OpenSSL is an open source implementation of the SSL and TLS protocols.

Daniel Bleichenbacher recently described an attack on PKCS #1 v1.5 signatures. If an RSA key with exponent 3 is used it may be possible to forge a PKCS #1 v1.5 signature signed by that key. Implementations may incorrectly verify the certificate if they are not checking for excess data in the RSA exponentiation result of the signature.

Since there are CAs using exponent 3 in wide use, and PKCS #1 v1.5 is used in X.509 certificates, all software that uses OpenSSL to verify X.509 certificates is potentially vulnerable, as well as any other use of PKCS #1 v1.5. This includes software that uses OpenSSL for SSL or TLS.

NOTE: OpenSSL versions up to 0.9.7j and 0.9.8b are affected.

=> Upgrade your OpenSSL

=> More about the signature forgery technique

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