James Ralston discovered that the sasl_encode64() function of cyrus-sasl2, a free library implementing the Simple Authentication and Security Layer, suffers from a missing null termination in certain situations. This causes several buffer overflows in situations where cyrus-sasl2 itself requires the string to be null terminated which can lead to denial of service or arbitrary code execution. Important notice (Quoting from US-CERT): While this patch will fix currently vulnerable code, it can cause non-vulnerable existing code to break. Here's a function prototype from include/saslutil.h to clarify my explanation: Assume a scenario where calling code has been written in such a way that it calculates the exact size required for base64 encoding in advance, then allocates a buffer of that exact size, passing a pointer to the buffer into sasl_encode64() as *out. As long as this code does not anticipate that the buffer is NUL-terminated (does not call any string-handling functions like strlen(), for example) the code will work and it will not be vulnerable. Once this patch is applied, that same code will break because sasl_encode64() will begin to return SASL_BUFOVER.