Forgot to escape backslashes.

guacamole/proxy/protocol.c

@@ -19,10 +19,8 @@ char* guac_escape_string(const char* str) {
         switch (str[i]) {
 
             case ';':
-                length += 2;
-                break;
-
             case ',':
+            case '\\':
                 length += 2;
                 break;
 
@@ -49,6 +47,11 @@ char* guac_escape_string(const char* str) {
                 *(current++) = 'c';
                 break;
 
+            case '\\':
+                *(current++) = '\\';
+                *(current++) = '\\';
+                break;
+
             default:
                 *(current++) = str[i];
         }