PuTTY on Windows crashes whenever I copy a selection of roughly 100 or more lines containing UTF-8 characters, especially box-drawing symbols such as ├─ and bullet characters. The issue occurs with automatic selection copying, Ctrl+Insert, and the right-click Copy action.
I reproduced it by connecting to Linux, running `fwupdmgr get-devices`, selecting the output, and copying it. The crash happens with PuTTY 0.76, 0.78, and 0.85, on both 32-bit and 64-bit builds. I have tried different fonts, changing terminal, window, selection, and SSH-bug settings, disabling automatic clipboard copying, running as Administrator, and using `-restrict-acl`. The problem also occurs on Windows 10 without any third-party clipboard manager. Increasing scrollback has no effect.
The Windows event log reports an access violation (`0xc0000005`) in `ntdll.dll`. Logging the session to a text file works, but it is not a practical replacement for copying selected text directly. Has anyone encountered this, or found a setting that prevents the crash?
4 Answers
The crash is probably not caused by the font or scrollback size. The important setting turned out to be PuTTY's “copy in clipboard RTF” option. Disabling RTF clipboard copying prevents the crash, presumably by avoiding the code path that converts the selected UTF-8 text into rich-text clipboard data. It is worth checking the saved session and default settings, since this option may be enabled unexpectedly.
Switching to OpenSSH with Windows Terminal is one possible long-term alternative, but it does not directly replace the whole PuTTY setup for everyone. People may depend on saved PuTTY sessions, Pageant-managed keys, PSCP, PSFTP, serial connections, or existing scripts. Fixing the clipboard setting is much less disruptive if the rest of the ecosystem is working well.
Trying Safe Mode, changing DEP settings, or increasing the scrollback buffer may help rule out environmental problems, but none of those address the actual cause here. Since the crash happens during copying and disappears when RTF clipboard copying is disabled, the clipboard format conversion is the useful lead.
A workable fallback is to log the session to a text file and copy the needed text from there. It avoids PuTTY's clipboard conversion path, although it is understandably less convenient than copying directly from the terminal.
Logging does capture the output, but I only want to copy selected portions when needed. I also noticed some invisible non-breaking-space characters, so I suspected the clipboard conversion.
Exactly. PuTTY is small, portable, and often integrated into years of automation. Replacing it is not simply a matter of installing another terminal, especially when file-transfer tools and key management are involved.