1 files changed, 25 insertions, 1 deletions

diff --git a/plugins/check_ssh.c b/plugins/check_ssh.c
index 8a3abb03..b4bfab45 100644
--- a/plugins/check_ssh.c
+++ b/plugins/check_ssh.c
@@ -278,11 +278,35 @@ ssh_connect (char *haddr, int hport, char *remote_version, char *remote_protocol
                 printf("SSH CRITICAL - No version control string received");
                 exit(STATE_CRITICAL);
         }
+        /*
+         * "When the connection has been established, both sides MUST send an
+         * identification string.  This identification string MUST be
+         *
+         * SSH-protoversion-softwareversion SP comments CR LF"
+         *              - RFC 4253:4.2
+         */
         strip (version_control_string);
         if (verbose)
                 printf ("%s\n", version_control_string);
         ssh_proto = version_control_string + 4;
-        ssh_server = ssh_proto + strspn (ssh_proto, "-0123456789.");
+
+        /*
+         * We assume the protoversion is of the form Major.Minor, although
+         * this is not _strictly_ required. See
+         *
+         * "Both the 'protoversion' and 'softwareversion' strings MUST consist of
+         * printable US-ASCII characters, with the exception of whitespace
+         * characters and the minus sign (-)"
+         *              - RFC 4253:4.2
+         * and,
+         *
+         * "As stated earlier, the 'protoversion' specified for this protocol is
+         * "2.0".  Earlier versions of this protocol have not been formally
+         * documented, but it is widely known that they use 'protoversion' of
+         * "1.x" (e.g., "1.5" or "1.3")."
+         *              - RFC 4253:5
+         */
+        ssh_server = ssh_proto + strspn (ssh_proto, "0123456789.") + 1; /* (+1 for the '-' separating protoversion from softwareversion) */
 
         /* If there's a space in the version string, whatever's after the space is a comment
          * (which is NOT part of the server name/version)*/