Better docs for DisableTrivialAuth

2 files changed, 27 insertions, 6 deletions

diff --git a/CHANGES b/CHANGES
index 9d9d480..457cb52 100644
--- a/CHANGES
+++ b/CHANGES
@@ -40,7 +40,7 @@ Features and Changes:
 - Improve permission error message
   Patch from k-kurematsu
 
-2022.82 regression fixes:
+Regression fixes from 2022.82:
 
 - Fix X11 build
 
@@ -155,10 +155,13 @@ Features and Changes:
   Patch from Raphaël Hertzog
   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903403
 
-- Added client option "-o DisableTrivialAuth". This can be used to prevent
-  the server immediately accepting successful authentication (before any auth
-  request) which could cause UI confusion and security issues with agent
-  forwarding - it isn't clear which host is prompting to use a key.
+- Added client option "-o DisableTrivialAuth". It disallows a server immediately
+  giving successful authentication (without presenting any password/pubkey prompt).
+  This avoids a UI confusion issue where it may appear that the user is accepting
+  a SSH agent prompt from their local machine, but are actually accepting a prompt
+  sent immediately by the remote server. 
+  CVE-2021-36369 though the description there is a bit confused. It only applies
+  to Dropbear as a client.
   Thanks to Manfred Kaiser from Austrian MilCERT
 
 - Add -q client option to hide remote banner, from Hans Harder
diff --git a/dbclient.1 b/dbclient.1
index fbbbc1b..8a916dc 100644
--- a/dbclient.1
+++ b/dbclient.1
@@ -94,7 +94,18 @@ is performed at all, this is usually undesirable.
 .B \-A
 Forward agent connections to the remote host. dbclient will use any
 OpenSSH-style agent program if available ($SSH_AUTH_SOCK will be set) for
-public key authentication.  Forwarding is only enabled if -A is specified.
+public key authentication.  Forwarding is only enabled if \fI-A\fR is specified.
+
+Beware that a forwarded agent connection will allow the remote server to have
+the same authentication credentials as you have used locally. A compromised
+remote server could use that to log in to other servers. 
+
+In many situations Dropbear's multi-hop mode is a better and more secure alternative
+to agent forwarding, avoiding having to trust the intermediate server.
+
+If the SSH agent program is set to prompt when a key is used, the 
+\fI-o DisableTrivialAuth\fR option can prevent UI confusion.
+
 .TP
 .B \-W \fIwindowsize
 Specify the per-channel receive window buffer size. Increasing this 
@@ -159,6 +170,13 @@ Send dbclient log messages to syslog in addition to stderr.
 .TP
 .B Port
 Specify a listening port, like the \fI-p\fR argument.
+.TP
+.B DisableTrivialAuth
+Disallow a server immediately
+giving successful authentication (without presenting any password/pubkey prompt).
+This avoids a UI confusion issue where it may appear that the user is accepting
+a SSH agent prompt from their local machine, but are actually accepting a prompt
+sent immediately by the remote server. 
 .RE
 .TP
 .B \-s