libpq: Bail out during SSL/GSS negotiation errors

This commit changes libpq so that errors reported by the backend during
the protocol negotiation for SSL and GSS are discarded by the client, as
these may include bytes that could be consumed by the client and write
arbitrary bytes to a client's terminal.

A failure with the SSL negotiation now leads to an error immediately
reported, without a retry on any other methods allowed, like a fallback
to a plaintext connection.

A failure with GSS discards the error message received, and we allow a
fallback as it may be possible that the error is caused by a connection
attempt with a pre-11 server, GSS encryption having been introduced in
v12.  This was a problem only with v17 and newer versions; older
versions discard the error message already in this case, assuming a
failure caused by a lack of support for GSS encryption.

Author: Jacob Champion
Reviewed-by: Peter Eisentraut, Heikki Linnakangas, Michael Paquier
Security: CVE-2024-10977
Backpatch-through: 12

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index a22c8520c004b4fe33b580ec63499635e0cdbb38..812c07e500f2566edcf796407d133e37b3ec5cd7 100644 (file)
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -1521,10 +1521,10 @@ SELCT 1/0;
 
    
     The frontend should also be prepared to handle an ErrorMessage
-    response to SSLRequest from the server.  This would only occur if
-    the server predates the addition of SSL support
-    to PostgreSQL.  (Such servers are now very ancient,
-    and likely do not exist in the wild anymore.)
+    response to SSLRequest from the server. The frontend should not display
+    this error message to the user/application, since the server has not been
+    authenticated
+    (CVE-2024-10977).
     In this case the connection must
     be closed, but the frontend might choose to open a fresh connection
     and proceed without requesting SSL.
@@ -1597,12 +1597,13 @@ SELCT 1/0;
 
    
     The frontend should also be prepared to handle an ErrorMessage
-    response to GSSENCRequest from the server.  This would only occur if
-    the server predates the addition of GSSAPI encryption
-    support to PostgreSQL.  In this case the
-    connection must be closed, but the frontend might choose to open a fresh
-    connection and proceed without requesting GSSAPI
-    encryption.
+    response to GSSENCRequest from the server.  The frontend should not display
+    this error message to the user/application, since the server has not been
+    authenticated
+    (CVE-2024-10977).
+    In this case the connection must be closed, but the frontend might choose
+    to open a fresh connection and proceed without requesting
+    GSSAPI encryption.
    
 
    

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 70abfc049ff185df7146dc891b82a9742fc25fe0..be028d628b1b32ee83af1d06dc1563d4e400504c 100644 (file)
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3056,16 +3056,13 @@ keep_going:                     /* We will come back to here until there is
                    {
                        /*
                         * Server failure of some sort, such as failure to
-                        * fork a backend process.  We need to process and
-                        * report the error message, which might be formatted
-                        * according to either protocol 2 or protocol 3.
-                        * Rather than duplicate the code for that, we flip
-                        * into AWAITING_RESPONSE state and let the code there
-                        * deal with it.  Note we have *not* consumed the "E"
-                        * byte here.
+                        * fork a backend process.  Don't bother retrieving
+                        * the error message; we should not trust it as the
+                        * server has not been authenticated yet.
                         */
-                       conn->status = CONNECTION_AWAITING_RESPONSE;
-                       goto keep_going;
+                       appendPQExpBuffer(&conn->errorMessage,
+                                         libpq_gettext("server sent an error response during SSL exchange\n"));
+                       goto error_return;
                    }
                    else
                    {