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elyograg
Asked: 2022-03-27 07:29:20 +0800 CST

Key forwarding with putty isn't working, but plink DOES work

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I'm having a problem where putty's key forwarding (via pageant) to my gitlab server isn't working. I'm doing a putty session to my server, with ssh auth forwarding enabled. I see the effects of that forwarding in the environment variables on the remote system.

Here's a transcript from an attempt that is not working. This is in a putty window.

login as: elyograg
Authenticating with public key "elyograg-home" from agent
elyograg@smeagol:~$ cd /etc/haproxy
elyograg@smeagol:/etc/haproxy$ git pull
[email protected]'s password:             (at this point I did Ctrl-C)
elyograg@smeagol:/etc/haproxy$ env | grep SSH
SSH_AUTH_SOCK=/tmp/ssh-PaSFdm2LDk/agent.3816409
SSH_CONNECTION=192.168.1.222 58109 192.168.1.200 22
SSH_CLIENT=192.168.1.222 58109 22
SSH_TTY=/dev/pts/0

The "git pull" command should have authenticated instantly with no password via the key forwarding. This HAS worked in the past.

What's really weird here is that Eclipse and Git for Windows, which both utilize plink (part of the putty install), are working just fine to the same gitlab server with the exact same keys. The plink program uses the same agent forwarding mechanisms as putty. So I know that it's not a matter of using the wrong key. I had putty version 0.76 installed, which is the latest release version at this time. I installed a pre-release 0.77 version with no change in behavior.

I'm on 64-bit Windows 10, fully up to date. CPU doesn't support Windows 11. The server where I am trying this is 64-bit Ubuntu Server 20.04, also fully up to date, running on a Dell R720xd.

I tried to find a support resource for putty, but it looks like they don't have one. They've listed a couple of usenet groups for general ssh discussion.

putty git gitlab plink

1 Answers

  1. Downgrading to putty 0.74 fixed the problem. I will see about filing a bug on putty. I also tried 0.75 which didn't work.

    edit:

    I got in touch with the putty project. It's a problem they know about and have fixed. It is very likely that I had forgotten to close pageant before I did the 0.77pre upgrade. Both pageant and putty have to be upgraded to get the bugfix. I did the upgrade again, making absolutely sure that I stopped pageant, and now it's all working on that pre-release version.

    https://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/win-handle-use-after-close.html

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