OpenSSL CMS And S/MIME Bleichenbacher Attack Vulnerability
26 Mar. 2012
Summary
The implementation of Cryptographic Message Syntax (CMS) and PKCS #7 in OpenSSL before 0.9.8u and 1.x before 1.0.0h does not properly restrict certain oracle behavior, which makes it easier for context-dependent attackers to decrypt data via a Million Message Attack (MMA) adaptive chosen ciphertext attack.
Vulnerable Systems:
* Cryptographic Message Syntax (CMS) and PKCS #7 in OpenSSL before 0.9.8u and 1.x before 1.0.0h
A weakness in the OpenSSL CMS and PKCS #7 code can be exploited
using Bleichenbacher's attack on PKCS #1 v1.5 RSA padding
also known as the million message attack (MMA).
Only users of CMS, PKCS #7, or S/MIME decryption operations are affected. A
successful attack needs on average 2^20 messages. In practice only automated
systems will be affected as humans will not be willing to process this many
messages.
SSL/TLS applications are *NOT* affected by this problem since the
SSL/TLS code does not use the PKCS#7 or CMS decryption code.
Vendor Status:
OpenSSL core team had issued an update for this vulnerability
