Issue summary: During processing of a crafted CMS EnvelopedData message
with KeyAgreeRecipientInfo a NULL pointer dereference can happen.

Impact summary: Applications that process attacker-controlled CMS data may
crash before authentication or cryptographic operations occur resulting in
Denial of Service.

When a CMS EnvelopedData message that uses KeyAgreeRecipientInfo is
processed, the optional parameters field of KeyEncryptionAlgorithmIdentifier
is examined without checking for its presence. This results in a NULL
pointer dereference if the field is missing.

Applications and services that call CMS_decrypt() or PKCS7_decrypt()
on untrusted input (e.g., S/MIME processing or CMS-based protocols)
are vulnerable.