An invalid pointer dereference on read can be triggered when an application tries to load malformed PKCS7 data with the d2iPKCS7(), d2iPKCS7bio() or d2iPKCS7_fp() functions.
The result of the dereference is an application crash which could lead to a denial of service attack. The TLS implementation in OpenSSL does not call this function however third party applications might call these functions on untrusted data.