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ssh2_scan_kexinits must check to see whether it's behaving as an SSH client or server, in order to decide whether to look for "ext-info-s" in the server's KEXINIT or "ext-info-c" in the client's, respectively. This check was done by testing the pointer 'server_hostkeys' to see if it was non-NULL. I think I must have imagined that a variable of that name meant "the host keys we have available to offer the client, if we are the server", as the similarly named parameter 'our_hostkeys' in write_kexinit_lists in fact does mean. So I expected it to be non-NULL for the server and NULL for the client, and coded accordingly. But in fact it's used by the client: it collects host key types the client has _seen_ from the server, in order to offer them as cross- certification actions in the specials menu. Moreover, it's _always_ non-NULL, because in the server, it's easier to leave it present but empty than to get rid of it. So this code was always behaving as if it was the server, i.e. it was looking for "ext-info-c" in the client KEXINIT. When it was in fact the client, that test would always succeed, because we _sent_ that KEXINIT ourselves! But nobody ever noticed, because when we're the client, it doesn't matter whether we saw "ext-info-c", because we don't have any reason to send EXT_INFO from client to server. We're only concerned with server-to-client EXT_INFO. So this embarrassing bug had no actual effect.
This is the README for PuTTY, a free Windows and Unix Telnet and SSH
client.
PuTTY is built using CMake <https://cmake.org/>. To compile in the
simplest way (on any of Linux, Windows or Mac), run these commands in
the source directory:
cmake .
cmake --build .
Then, to install in the simplest way on Linux or Mac:
cmake --build . --target install
On Unix, pterm would like to be setuid or setgid, as appropriate, to
permit it to write records of user logins to /var/run/utmp and
/var/log/wtmp. (Of course it will not use this privilege for
anything else, and in particular it will drop all privileges before
starting up complex subsystems like GTK.) The cmake install step
doesn't attempt to add these privileges, so if you want user login
recording to work, you should manually ch{own,grp} and chmod the
pterm binary yourself after installation. If you don't do this,
pterm will still work, but not update the user login databases.
Documentation (in various formats including Windows Help and Unix
`man' pages) is built from the Halibut (`.but') files in the `doc'
subdirectory. If you aren't using one of our source snapshots,
you'll need to do this yourself. Halibut can be found at
<https://www.chiark.greenend.org.uk/~sgtatham/halibut/>.
The PuTTY home web site is
https://www.chiark.greenend.org.uk/~sgtatham/putty/
If you want to send bug reports or feature requests, please read the
Feedback section of the web site before doing so. Sending one-line
reports saying `it doesn't work' will waste your time as much as
ours.
See the file LICENCE for the licence conditions.