Integer overflow in the stralloc_readyplus function in qmail, when running on 64 bit platforms with a large amount of virtual memory, allows remote attackers to cause a denial of service and possibly execute arbitrary code via a large SMTP request.
The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.