PuTTY before 0.73 mishandles the "bracketed paste mode" protection mechanism, which may allow a session to be affected by malicious clipboard content.

PuTTY before 0.73 might allow remote SSH-1 servers to cause a denial of service by accessing freed memory locations via an SSH1_MSG_DISCONNECT message.

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 client).