PuTTY 0.68 through 0.73 has an Observable Discrepancy leading to an information leak in the algorithm negotiation. This allows man-in-the-middle attackers to target initial connection attempts (where no host key for the server has been cached by the

In PuTTY versions before 0.71 on Windows, local attackers could hijack the application by putting a malicious help file in the same directory as the executable.

Potential recycling of random numbers used in cryptography exists within PuTTY before 0.71.

Multiple denial-of-service attacks that can be triggered by writing to the terminal exist in PuTTY versions before 0.71.

A remotely triggerable memory overwrite in RSA key exchange in PuTTY before 0.71 can occur before host key verification.

In PuTTY versions before 0.71 on Unix, a remotely triggerable buffer overflow exists in any kind of server-to-client forwarding.