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putty/buster-backports

  • package: putty/buster-backports
  • releases: buster

Current state:

The package is affected by CVE-2023-48795 (terrapin attack). Buster was patched by backporting fix from sid

Moreover it was affected by CVE-2021-36367 (no-dsa) and CVE-2020-14002 (no-dsa)

putty is a GUI tool so backporting is hard. Files are moving and gui code is changing.

There is a tentative of backport here https://salsa.debian.org/lts-team/packages/putty/-/commits/buster

Obstacles Preventing Continued Support

The code is a cryptographic code so particularly sensible security wise.

For bullseye it was possible to backport. This patch does not apply cleanly and some upstream support was needed.
However for buster even this supplementary API need other patches exposing to risk of regression in security sensitive context.

Alternative Course of Action

CVE-2023-48795 is not ignorable.

Other option is to disable in the library ChaCha20-Poly1305 and MACs which use Encrypt-then-MAC,but in this case it may break users

Potential Impacts

Impacts of taking no action

User using putty are vulnerable to terrapin action as client on buster.

Additional impact

Changelog between 0.70 (buster) and 0.74 is small, and mainly bug fixes/security fixes

These features were new in 0.74 (released 2020-06-27):

  • 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.

These features were new in 0.73 (released 2019-09-29):

  • Security fix: on Windows, other applications were able to bind to the same TCP port as a PuTTY local port forwarding.
  • Security fix: in bracketed paste mode, the terminal escape sequences that should delimit the pasted data were appearing together on one side of it, making it possible to misidentify pasted data as manual keyboard input.
  • Bug fix (possibly security-related): an SSH-1 server sending a disconnection message could cause an access to freed memory.
  • Bug fix: Windows Plink would crash on startup if it was acting as a connection-sharing downstream.
  • Bug fix: Windows PuTTY now updates its terminal window size correctly if the screen resolution changes while it's maximised.
  • Bug fix: tweaked terminal handling to prevent lost characters at the ends of lines in gcc's coloured error messages.
  • Bug fix: removed a bad interaction between the 'clear scrollback' operation and mouse selection that could give rise to the dreaded "line==NULL" assertion box.

These features were new in 0.72 (released 2019-07-20):

  • Security fixes found by the EU-funded bug bounty:
    • two separate vulnerabilities affecting the obsolete SSH-1 protocol, both available before host key checking
    • a vulnerability in all the SSH client tools (PuTTY, Plink, PSFTP and PSCP) if a malicious program can impersonate Pageant
  • Bug fix: crash in GSSAPI / Kerberos key exchange affecting third-party GSSAPI providers on Windows (such as MIT Kerberos for Windows)
  • Bug fix: crash in GSSAPI / Kerberos key exchange triggered if the server provided an ordinary SSH host key as part of the exchange
  • Bug fix: trust sigils were never turned off in SSH-1 or Rlogin
  • Bug fix: trust sigils were never turned back on if you used Restart Session
  • Bug fix: PSCP in SCP download mode could create files with a spurious newline at the end of their names
  • Bug fix: PSCP in SCP download mode with the -p option would generate spurious complaints about illegal file renaming
  • Bug fix: the initial instruction message was never printed during SSH keyboard-interactive authentication
  • Bug fix: pasting very long lines through connection sharing could crash the downstream PuTTY window
  • Bug fix: in keyboard layouts with a ',' key on the numeric keypad (e.g. German), Windows PuTTY would generate '.' instead for that key
  • Bug fix: PuTTYgen could generate RSA keys with a modulus one bit shorter than requested

These features were new in 0.71 (released 2019-03-16):

  • Security fixes found by an EU-funded bug bounty programme:
    • a remotely triggerable memory overwrite in RSA key exchange, which can occur before host key verification
    • potential recycling of random numbers used in cryptography
    • on Windows, hijacking by a malicious help file in the same directory as the executable
    • on Unix, remotely triggerable buffer overflow in any kind of server-to-client forwarding
    • multiple denial-of-service attacks that can be triggered by writing to the terminal
  • Other security enhancements: major rewrite of the crypto code to remove cache and timing side channels.
  • User interface changes to protect against fake authentication prompts from a malicious server.
  • We now provide pre-built binaries for Windows on Arm.
  • Hardware-accelerated versions of the most common cryptographic primitives: AES, SHA-256, SHA-1.
  • GTK PuTTY now supports non-X11 displays (e.g. Wayland) and high-DPI configurations.
  • Type-ahead now works as soon as a PuTTY window is opened: keystrokes typed before authentication has finished will be buffered instead of being dropped.
  • Support for GSSAPI key exchange: an alternative to the older GSSAPI authentication system which can keep your forwarded Kerberos credentials updated during a long session.
  • More choices of user interface for clipboard handling.
  • New terminal features: support the REP escape sequence (fixing an ncurses screen redraw failure), true colour, and SGR 2 dim text.
  • Pressing Ctrl+Shift+PgUp or Ctrl+Shift+PgDn now takes you straight to the top or bottom of the terminal scrollback.
Edited by Bastien Roucariès