Multiple weaknesses have been identified in PyDNS, a DNS client implementation for the Python language. Dan Kaminsky identified a practical vector of DNS response spoofing and cache poisoning, exploiting the limited entropy in a DNS transaction ID and lack of UDP source port randomization in many DNS implementations. Scott Kitterman noted that python-dns is vulnerable to this predictability, as it randomizes neither its transaction ID nor its source port. Taken together, this lack of entropy leaves applications using python-dns to perform DNS queries highly susceptible to response forgery. The Common Vulnerabilities and Exposures project identifies this class of weakness as CVE-2008-1447 and this specific instance in PyDNS as CVE-2008-4099.