PuTTY Release Notes

Security issue

fixed a remotely triggerable double-free in RSA key exchange. (We don't know of any way it is exploitable to execute code.)

Minor security issue: fixed a remotely triggerable crash in NIST ECDSA signature verification. (An assertion failure definitely not exploitable to execute code.)

Minor security issue: fixed marking of Telnet and Rlogin session data with a trust sigil after you authenticated to a proxy (possibly allowing a server to spoof a repeat proxy password prompt).

Ability to run a specified command before starting the connection, e.g. to perform wake-on-LAN or a port knock.

On Unix

display 'pre-edit text', showing the progress of using multiple keystrokes to compose a single Unicode character.

improved support for to running the GUI tools on Wayland (fixed startup issues and tuned performance).

Bug fix

configuring a SSH certificate authority on Unix would fail unless you manually made a config directory.

spurious "Network error: Socket is not connected" when authenticating to some HTTP proxies.

disabling cursor blinking in the Windows Control Panel but enabling it in PuTTY would lead to a tight loop.

Support for ML-KEM, the NIST-standardised post-quantum key exchange mechanism. (In addition to NTRU Prime, which has been supported since 0.78.)

Support for full Unicode file names in Windows file selector dialogs. (However, these do not yet round-trip through a saved session.)

Bug fix: psftp -b works again.

Bug fix: assertion failure if an SSH connection times out at the login prompt.

Bug fix: crash in Pageant if an SSH connection is abandoned while waiting for a deferred decryption passphrase.

Bug fix: tight loop if PuTTY tried to send an empty answerback string.

Bug fix: accidental truncation of some configuration edit boxes' contents to 127 characters.

Bug fix: Windows XP support was accidentally broken, and now reinstated.

Bug fix: restored interoperation with third-party tools that auto-fill login prompts by sending ^M for Return.

Bug fix: confusion when terminal window resized by tools like FancyZones.

Bug fix: the small keypad keys didn't reliably work in the terminal on Unix.

Major refactoring of Unicode handling to allow the use of 'foreign' Unicode characters, i.e. outside the system's configured default character set / code page. Not yet complete, but the following things work:

• Windows console: usernames and passwords entered interactively into PSCP, PSFTP and Plink can use foreign characters.
• Windows command line: usernames, remote commands, and filenames entered via command-line options can use foreign characters.
• PuTTY's own terminal (on Windows and Unix): even if it's not configured into UTF-8 mode for the main session, interactive usernames and passwords can use foreign characters.
• Unicode version update: all character analysis is updated to Unicode 16.0.0.
• Unicode terminal rendering: national and regional flags are now understood by PuTTY's terminal emulator. (However, correct display of those flags will depend on fonts and operating system.)
• The Event Log mentions the local address and port number of the outgoing connection socket.
• Bracketed paste mode can now be turned off in the Terminal > Features panel.
• Unix Pageant: new --foreground mode for running as a subprocess.
• Bug fix: the 'border width' configuration option is now honoured even when the window is maximised.
• Bug fix: SHA-2 based RSA signatures are now sent with correct zero padding.
• Bug fix: terminal wrap mishandling caused occasional incorrect redraws in curses-based applications.
• Bug fix: Alt + function key in "Xterm 216+" mode sent a spurious extra escape character.

Windows installer scope is back to the normal 'per machine' setting, reverting 0.78's security workaround.

Note: this means that installing the 0.79 or later Windows installer will not automatically uninstall 0.78, if 0.78 was installed using its default 'per user' scope. In that situation we recommend uninstalling 0.78 first, if possible. If both end up installed, uninstalling both and then re-installing the new version will fix things up.

Terminal mouse tracking: support for mouse movements which are not drags.

Terminal mouse tracking: support for horizontal scroll events (e.g. generated by trackpads).

Backwards compatibility fix: certificate-based user authentication now works with OpenSSH 7.7 and earlier.

Bug fix: in a session using the 'Raw' protocol, pressing ^D twice in the terminal window could cause an assertion failure.

Bug fix: terminal output could hang if a resize control sequence was sent by the server (and was not disabled in the Features panel) but PuTTY's window was set to non-resizable in the Window panel.

Bug fix: GTK PuTTY could fail an assertion if a resize control sequence was sent by the server while the window was docked to one half of the screen in KDE.

Bug fix: GTK PuTTY could fail an assertion if you tried to change the font size while the window was maximised.

Bug fix: the 'bell overload' timing settings were misinterpreted by Unix PuTTY and pterm 0.77/0.78; if any settings were saved using these versions, confusion can persist with newer versions.

Bug fix: SSH authentication banners were not reliably printed if a server sent one immediately before closing the connection (e.g. intended as a user-visible explanation for the connection closure).

Bug fix: the 'close' command in PSFTP always reported failure, so that ending a psftp -b batch script with it would cause PSFTP as a whole to believe it had failed, even if everything worked fine.

Bug fix: certificate handling would do the wrong thing, for RSA keys only, if you specified a detached certificate to go with a PPK file that had a different certificate embedded.

Bug fix: Windows Pageant's option to write out a configuration file fragment for Windows OpenSSH now works even if you have a space in your user name.

Bug fix: in local-line-editing mode, pressing ^U now just clears the line, instead of clearing it and then inserting a literal ^U.

Several bug fixes in edge cases of terminal wrapping, involving double-width characters.

Windows installer scope was changed to 'per user' instead of the correct 'per machine'. This was a workaround for a Windows security issue, now fixed. It causes many other problems, so if you need to install 0.78, we recommend running msiexec.exe by hand with ALLUSERS=1 on the command line.

Support for OpenSSH certificates, for both user authentication keys and host keys.

New SSH proxy modes, for running a custom shell command or subsystem on the proxy server instead of forwarding a port through it.

New plugin system to allow a helper program to provide responses in keyboard-interactive authentication, intended to automate one-time password systems.

Support for NTRU Prime post-quantum key exchange.

Support for AES-GCM (in the OpenSSH style rather than RFC 5647).

Support for more forms of Diffie-Hellman key exchange: new larger integer groups (such as group16 and group18), and support for using those and ECDH with GSSAPI.

SSH configuration panels slightly reorganised. In particular, the configuration option 'Private key file for authentication' has moved to a new 'Credentials' panel alongside controls for some of the above new features.

Bug fix: the 32-bit Windows build now runs on Windows XP again.

Bug fix: server-controlled window title setting now works again even if the character set is ISO 8859 (or a few other affected single-byte character sets).

Bug fix: certain forms of OSC escape sequences (sent by some real servers) could cause PuTTY to crash.

Bug fix: the -pwfile / -pw options no longer affect local key passphrase prompts, and no longer suppress Plink's anti-spoofing measures.

Major improvements to network proxy support:

Support for interactively prompting the user if the proxy server requires authentication.

Built-in support for proxying via another SSH server, so that PuTTY will SSH to the proxy and then automatically forward a port through it to the destination host. (Similar to running plink -nc as a subprocess, but more convenient to set up, and allows you to answer interactive prompts presented by the proxy.)

Support for HTTP Digest authentication, when talking to HTTP proxies.

Introduced pterm.exe, a PuTTY-like wrapper program for Windows command prompts (or anything else running in a Windows console). Not yet included in the installer, but available as a .exe file from the Download page.

Updated Unicode and bidi support to Unicode 14.0.0.

New command-line option -pwfile, like -pw except that it reads the password from a file so that it doesn't show up on the command line.

Windows Pageant: option --openssh-config to allow easy interoperation with Windows's ssh.exe.

-pw (and -pwfile) now do not fall back to interactively prompting for a password if the provided password fails. (That was the original intention.)

New configuration options for keyboard handling:

• Option to control handling of Shift + arrow keys
• Extra mode in the function-keys option, for modern xterm (v216 and above).

Bug workaround flag to wait for the server's SSH greeting before sending our own, for servers (or proxies) that lose outgoing data before seeing any incoming data.

Crypto update: added side-channel resistance in probabilistic RSA key generation.

Crypto update: retired the use of short Diffie-Hellman exponents (just in case).

Bug fix: reconfiguring remote port forwardings more than once no longer crashes.

Bug fix: terminal output processing is now paused while handling a remote-controlled terminal resize, so that the subsequent screen redraw is interpreted relative to the new terminal size instead of the old.

Bug fix: Windows PuTTYgen's mouse-based entropy collection now handles high-frequency mice without getting confused.

Bug fix: Windows Pageant can now handle large numbers of concurrent connections without hanging or crashing.

Bug fix: if Windows Pageant is started multiple times simultaneously, the instances should reliably agree on one of them to be the persistent server.

Bug fix: remote-controlled changes of window title are now interpreted according to the configured character set.

Bug fix: remote-controlled changes of window title no longer get confused by UTF-8 characters whose encoding includes the byte 0x9C (which terminates the control sequence in non-UTF-8 contexts).

Bug fix: popping up the window context menu in the middle of a drag-select now no longer leaves the drag in a stuck state.

Bug fix: extensive use of true colour in the terminal no longer slows down window redraws unnecessarily.

Bug fix: when PSCP reports the server sending a disallowed compound pathname, it correctly reports the replacement name it's using for the downloaded file.

Bug fix: enabling X11 forwarding in psusan failed to fall back through possible port numbers for the forwarded X display.

For developers:

Migrated the build system to CMake, removing the old idiosyncratic mkfiles.pl and the autotools system.

New option to abandon an SSH connection if the server allows you to authenticate in a trivial manner.

Bug fix: Windows PuTTY crashed when the 'Use system colours' option was used.

Bug fix: crash on Windows when using MIT Kerberos together with 'Restart Session'.

Bug fix: Windows PuTTY leaked named pipes after contacting Pageant.

Bug fix: Windows PuTTY didn't update the window while you held down the scrollbar arrow buttons long enough to 'key-repeat'.

Bug fix: user colour-palette reconfiguration via 'Change Settings' were delayed-action.

Bug fix: server colour-palette reconfigurations were sometimes lost.

Bug fix: a tight loop could occur on reading a truncated private key file.

Bug fix: the Windows Pageant GUI key list didn't display key lengths.

Security fix: on Windows, a server could DoS the whole Windows GUI by telling the PuTTY window to change its title repeatedly at high speed.

Pageant now supports loading a key still encrypted, and decrypting it later by prompting for the passphrase on first use.

Upgraded default SSH key fingerprint format to OpenSSH-style SHA-256.

Upgraded private key file format to PPK3, with improved passphrase hashing and no use of SHA-1.

Support for RSA key algorithms using SHA-2 instead of SHA-1.

Support for Curve448 key exchange and Ed448 public keys.

Terminal now supports ESC [ 9 m for strikethrough text.

New protocols: bare ssh-connection layer for use over already-secure IPC channels, and SUPDUP for talking to very old systems such as PDP-10s.

PuTTYgen now supports alternative provable-prime generation algorithm for RSA and DSA.

The Unix tools can now connect directly to a Unix-domain socket.