4.27 The Bugs and More Bugs panels

Not all SSH servers work properly. Various existing servers have bugs in them, which can make it impossible for a client to talk to them unless it knows about the bug and works around it.

Since most servers announce their software version number at the beginning of the SSH connection, PuTTY will attempt to detect which bugs it can expect to see in the server and automatically enable workarounds. However, sometimes it will make mistakes; if the server has been deliberately configured to conceal its version number, or if the server is a version which PuTTY's bug database does not know about, then PuTTY will not know what bugs to expect.

The Bugs and More Bugs panels (there are two because we have so many bug compatibility modes) allow you to manually configure the bugs PuTTY expects to see in the server. Each bug can be configured in three states:

• ‘Off’: PuTTY will assume the server does not have the bug.
• ‘On’: PuTTY will assume the server does have the bug.
• ‘Auto’: PuTTY will use the server's version number announcement to try to guess whether or not the server has the bug. (This option is not available for bugs that cannot be detected from the server version, e.g. because they must be acted on before the server version is known.)

(The PuTTY project has a defined policy about when we're prepared to add auto-detection for a bug workaround. See section B.6.)

• 4.27.1 ‘Chokes on SSH-2 ignore messages’
• 4.27.2 ‘Handles SSH-2 key re-exchange badly’
• 4.27.3 ‘Chokes on PuTTY's SSH-2 ‘winadj’ requests’
• 4.27.4 ‘Replies to requests on closed channels’
• 4.27.5 ‘Ignores SSH-2 maximum packet size’
• 4.27.6 ‘Discards data sent before its greeting’
• 4.27.7 ‘Chokes on PuTTY's full KEXINIT’
• 4.27.8 ‘Old RSA/SHA2 cert algorithm naming’
• 4.27.9 ‘Requires padding on SSH-2 RSA signatures’
• 4.27.10 ‘Only supports pre-RFC4419 SSH-2 DH GEX’
• 4.27.11 ‘Miscomputes SSH-2 HMAC keys’
• 4.27.12 ‘Misuses the session ID in SSH-2 PK auth’
• 4.27.13 ‘Miscomputes SSH-2 encryption keys’
• 4.27.14 ‘Chokes on SSH-1 ignore messages’
• 4.27.15 ‘Refuses all SSH-1 password camouflage’
• 4.27.16 ‘Chokes on SSH-1 RSA authentication’