An overflow can occur in the EVP_EncodeUpdate() function which is used for Base64 encoding of binary data. If an attacker is able to supply very large amounts of input data then a length check can overflow resulting in a heap corruption.
Internally to OpenSSL the EVP_EncodeUpdate() function is primarily used by the PEM_write_bio family of functions. These are mainly used within the OpenSSL command line applications. These internal uses are not considered vulnerable because all calls are bounded with length checks so no overflow is possible. User applications that call these APIs directly with large amounts of untrusted data may be vulnerable. (Note: Initial analysis suggested that the PEM_write_bio were vulnerable, and this is reflected in the patch commit message. This is no longer believed to be the case).
An overflow can occur in the EVP_EncryptUpdate() function. If an attacker is able to supply very large amounts of input data after a previous call to EVP_EncryptUpdate() with a partial block then a length check can overflow resulting in a heap corruption. Following an analysis of all OpenSSL internal usage of the EVP_EncryptUpdate() function all usage is one of two forms. The first form is where the EVP_EncryptUpdate() call is known to be the first called function after an EVP_EncryptInit(), and therefore that specific call must be safe. The second form is where the length passed to EVP_EncryptUpdate() can be seen from the code to be some small value and therefore there is no possibility of an overflow. Since all instances are one of these two forms, it is believed that there can be no overflows in internal code due to this problem. It should be noted that EVP_DecryptUpdate() can call EVP_EncryptUpdate() in certain code paths. Also EVP_CipherUpdate() is a synonym for EVP_EncryptUpdate(). All instances of these calls have also been analysed too and it is believed there are no instances in internal usage where an overflow could occur.
This could still represent a security issue for end user code that calls this function directly.
A MITM attacker can use a padding oracle attack to decrypt traffic when the connection uses an AES CBC cipher and the server support AES-NI.
This issue was introduced as part of the fix for Lucky 13 padding attack (CVE-2013-0169). The padding check was rewritten to be in constant time by making sure that always the same bytes are read and compared against either the MAC or padding bytes. But it no longer checked that there was enough data to have both the MAC and padding bytes.
When ASN.1 data is read from a BIO using functions such as d2i_CMS_bio() a short invalid encoding can cause allocation of large amounts of memory potentially consuming excessive resources or exhausting memory.
Any application parsing untrusted data through d2i BIO functions is affected. The memory based functions such as d2i_X509() are not affected. Since the memory based functions are used by the TLS library, TLS applications are not affected.
ASN1 Strings that are over 1024 bytes can cause an overread in applications using the X509_NAME_oneline() function on EBCDIC systems. This could result in arbitrary stack data being returned in the buffer.