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This is nice but the agent forwarding is a legitimate concern especially because a compromised host can take off with the private keys which are used while begi

by zippie 11y ago

This is nice but the agent forwarding is a legitimate concern especially because a compromised host can take off with the private keys which are used while beginning the session. Most private keys are used for more than connecting to a single host. In our setup we use jailkit allowing only ssh passthrough [1], we have added LDAP support to it (may release the patch later). [1] http://olivier.sessink.nl/jailkit/howtos_ssh_only.html http://olivier.sessink.nl/jailkit/howtos_ssh_only.html

joushou 11y ago
What authentication do you have from the jump host to the target? To me, it looks like it has been reduced to either none or keyboard-interactive (password) login, which is considered bad practice. I could very easily implement support for this in sshmux, providing the setup you seem to use, as a way to avoid agent forwarding, but I just genuinely did not expect anyone to use password authentication, apart from in default config scenarios, before a public key has been installed. Agent forwarding does not provide private keys, but only individual signing requests. This means that while the user is connected, and evil remote can request arbitrary signing, but only as long as the user is connected, and only as long as the users ssh agent is willing to do so. Using ssh-add -c further means that the user will have to accept each signing request. Also note that ssh -W, which is immune to any of these concerns, is fully supported by sshmux. Correct me if I'm wrong, but "Jailkit" does not seem to stop an evil legitimate user from poking around other hosts with forwarding and such (which they can as long as ssh -W functions, within the limits of what a firewall allows the jump host to do in general). sshmux allows you to lock users to targets, rather than lock general capabilities of the entire jump host. This is because, while I provide clients access to various hosts, I do not trust them enough to have any unnecessary privileges.

by zippie 11y ago

joushou 11y ago

What authentication do you have from the jump host to the target? To me, it looks like it has been reduced to either none or keyboard-interactive (password) login, which is considered bad practice. I could very easily implement support for this in sshmux, providing the setup you seem to use, as a way to avoid agent forwarding, but I just genuinely did not expect anyone to use password authentication, apart from in default config scenarios, before a public key has been installed. Agent forwarding does not provide private keys, but only individual signing requests. This means that while the user is connected, and evil remote can request arbitrary signing, but only as long as the user is connected, and only as long as the users ssh agent is willing to do so. Using ssh-add -c further means that the user will have to accept each signing request. Also note that ssh -W, which is immune to any of these concerns, is fully supported by sshmux. Correct me if I'm wrong, but "Jailkit" does not seem to stop an evil legitimate user from poking around other hosts with forwarding and such (which they can as long as ssh -W functions, within the limits of what a firewall allows the jump host to do in general). sshmux allows you to lock users to targets, rather than lock general capabilities of the entire jump host. This is because, while I provide clients access to various hosts, I do not trust them enough to have any unnecessary privileges.