PuTTY full changelog

Security fix for CVE-2024-31497: NIST P521 / ecdsa-sha2-nistp521 signatures are no longer generated with biased values of k. The previous bias compromises private keys.

Security fix: support for OpenSSH's new kex-strict protocol modification, addressing a vulnerability in some @openssh.com cipher and MAC modes, in particular ChaCha20+Poly1305.
Bug fix: the MSI-installed version of putty.exe can now find its help file again.
Bug fix: a server sending non-displaying terminal escape sequences such as ESC[0m now no longer resets the scrollback to the bottom of the window.

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.

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.
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.

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.)

PuTTY 0.73, released today, is a bug-fix release. It fixes a small number of bugs since 0.72, and a couple of them have potential security implications.

Security fix: an integer overflow bug in the agent forwarding code. See vuln-agent-fwd-overflow.
Security fix: the Windows PuTTY binaries should no longer be vulnerable to hijacking by specially named DLLs in the same directory (on versions of Windows where they previously were). See vuln-indirect-dll-hijack.
Windows PuTTY no longer sets a restrictive process ACL by default, because this turned out to inconvenience too many legitimate applications such as NVDA and TortoiseGit. You can still manually request a restricted ACL using the command-line option -restrict-acl.
The Windows PuTTY tools now come in a 64-bit version.
The Windows PuTTY tools now have Windows's ASLR and DEP security features turned on.
Support for elliptic-curve cryptography (the NIST curves and 25519), for host keys, user authentication keys, and key exchange.
Support for importing and exporting OpenSSH's new private key format.
Host key preference policy change: PuTTY prefers host key formats for which it already k