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New SSH bug flag, for 'can't handle SSH2_MSG_IGNORE'. Another user

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today reported an SSH2_MSG_UNIMPLEMENTED from a Cisco router which
looks as if it was triggered by SSH2_MSG_IGNORE, so I'm
experimentally putting this flag in. Currently must be manually
enabled, though if it turns out to solve the user's problem then
I'll probably add at least one version string...

[Edited commit message: actually, I also committed in error a piece
of experimental code as part of this checkin. Serve me right for not
running 'svn diff' first.]

[originally from svn r8926]
This commit is contained in:
Simon Tatham
2010-04-23 18:32:15 +00:00
parent 97ca111e29
commit d5aa23c116
7 changed files with 82 additions and 12 deletions
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20
doc/config.but
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@ -2948,9 +2948,6 @@ enabled when talking to a correct server, the session will succeed,
but keepalives will not work and the session might be more
vulnerable to eavesdroppers than it could be.
This is an SSH-1-specific bug. No known SSH-2 server fails to deal
with SSH-2 ignore messages.
\S{config-ssh-bug-plainpw1} \q{Refuses all SSH-1 \i{password camouflage}}
\cfg{winhelp-topic}{ssh.bugs.plainpw1}
@ -2992,6 +2989,23 @@ will be impossible.
This is an SSH-1-specific bug.
\S{config-ssh-bug-ignore2} \q{Chokes on SSH-2 \i{ignore message}s}
\cfg{winhelp-topic}{ssh.bugs.ignore2}
An ignore message (SSH_MSG_IGNORE) is a message in the SSH protocol
which can be sent from the client to the server, or from the server
to the client, at any time. Either side is required to ignore the
message whenever it receives it. PuTTY uses ignore messages in SSH-2
to confuse the encrypted data stream and make it harder to
cryptanalyse. It also uses ignore messages for connection
\i{keepalives} (see \k{config-keepalive}).
If it believes the server to have this bug, PuTTY will stop using
ignore messages. If this bug is enabled when talking to a correct
server, the session will succeed, but keepalives will not work and
the session might be less cryptographically secure than it could be.
\S{config-ssh-bug-hmac2} \q{Miscomputes SSH-2 HMAC keys}
\cfg{winhelp-topic}{ssh.bugs.hmac2}