PuTTY is a free implementation of Telnet and SSH for Windows and Unix platforms, along with an xterm terminal emulator. PuTTY is a client program for the SSH, Telnet and Rlogin network protocols.
These protocols are all used to run a remote session on a computer, over a network. PuTTY implements the client end of that session: the end at which the session is displayed, rather than the end at which it runs.
In really simple terms: you run PuTTY on a Windows machine, and tell it to connect to (for example) a Unix machine. PuTTY opens a window. Then, anything you type into that window is sent straight to the Unix machine, and everything the Unix machine sends back is displayed in the window. So you can work on the Unix machine as if you were sitting at its console, while actually sitting somewhere else.
- Security fix: if an SSH server accepted an offer of a public key and then rejected the signature, PuTTY could access freed memory, if the key had come from an SSH agent.
- Security feature: new config option to disable PuTTY’s dynamic host key preference policy, if you prefer to avoid giving away to eavesdroppers which hosts you have stored keys for.
- Bug fix: the installer UI was illegible in Windows high-contrast mode.
- Bug fix: console password input failed on Windows 7.
- Bug fixes in the terminal: one instance of the dreaded “line==NULL” error box, and two other assertion failures.
- Bug fix: potential memory-consuming loop in bug-compatible padding of an RSA signature from an agent.
- Bug fix: PSFTP’s buffer handling worked badly with some servers (particularly proftpd’s mod_sftp).
- Bug fix: cursor could be wrongly positioned when restoring from the alternate terminal screen. (A bug of this type was fixed in 0.59; this is a case that that fix missed.)
- Bug fix: character cell height could be a pixel too small when running GTK PuTTY on Ubuntu 20.04 (or any other system with a similarly up-to-date version of Pango).
- Bug fix: old-style (low resolution) scroll wheel events did not work in GTK 3 PuTTY. This could stop the scroll wheel working at all in VNC.
Legal Warning: Use of PuTTY, PSCP, PSFTP and Plink is illegal in countries where encryption is outlawed. I believe it is legal to use PuTTY, PSCP, PSFTP and Plink in England and Wales and in many other countries, but I am not a lawyer and so if in doubt you should seek legal advice before downloading it. You may find this site useful (it’s a survey of cryptography laws in many countries) but I can’t vouch for its correctness.
Use of the Telnet-only binary (PuTTYtel) is unrestricted by any cryptography laws.