This change breaks existing behavior.
Before, a missing ClientConfig.HostKeyCallback would cause host key
checking to be disabled. In this configuration, establishing a
connection to any host just works, so today, most SSH client code in
the wild does not perform any host key checks.
This makes it easy to perform a MITM attack:
* SSH installations that use keyboard-interactive or password
authentication can be attacked with MITM, thereby stealing
passwords.
* Clients that use public-key authentication with agent forwarding are
also vulnerable: the MITM server could allow the login to succeed, and
then immediately ask the agent to authenticate the login to the real
server.
* Clients that use public-key authentication without agent forwarding
are harder to attack unnoticedly: an attacker cannot authenticate the
login to the real server, so it cannot in general present a convincing
server to the victim.
Now, a missing HostKeyCallback will cause the handshake to fail. This
change also provides InsecureIgnoreHostKey() and FixedHostKey(key) as
ready made host checkers.
A simplistic parser for OpenSSH's known_hosts file is given as an
example. This change does not provide a full-fledged parser, as it
has complexity (wildcards, revocation, hashed addresses) that will
need further consideration.
When introduced, the host checking feature maintained backward
compatibility at the expense of security. We have decided this is not
the right tradeoff for the SSH library.
Fixesgolang/go#19767
Change-Id: I45fc7ba9bd1ea29c31ec23f115cdbab99913e814
Reviewed-on: https://go-review.googlesource.com/38701
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This allows the golang ssh-agent to support the full suite of keys
the library accepts.
Currently constraints are ignored.
Change-Id: I7d48c78e9a355582eb54788571a483a736c3d3ef
Reviewed-on: https://go-review.googlesource.com/21536
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Some ssh-agent clients expect the server to support remove all messages
for protocols 1 & 2 and error if protocol 1 support is missing.
This adds a null-op implementation of the remove all message in similar
fashion to the existing list all message support.
Fixesgolang/go#15159
Change-Id: I9389885d89c9147f3e10850893bba6ed7d0a4e82
Reviewed-on: https://go-review.googlesource.com/21468
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
The ssh-agent protocol allows the usage of keys and certs added to a
given agent to be constrained in certain ways. The only constraints
currently supported are lifetime (keys expire after some number of
seconds) and confirmation (the agent requires user confirmation before
performing any operations with the private key).
Change-Id: Idba5760db929805bf3da43fdcaca53ae6c479ca4
Reviewed-on: https://go-review.googlesource.com/12260
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
Reviewed-by: Peter Moody <pmoody@uber.com>
Han-Wen Nienhuys
Peter Moody
Peter Moody
Mark Severson
Andrew Gerrand
Adam Langley