Don't collapse multipart with a single sub-part inside multipart/signed parts.

1 files changed, 6 insertions, 1 deletions

diff --git a/Mailman/Handlers/MimeDel.py b/Mailman/Handlers/MimeDel.py
index ab7483ba..691a6e85 100644
--- a/Mailman/Handlers/MimeDel.py
+++ b/Mailman/Handlers/MimeDel.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2002-2011 by the Free Software Foundation, Inc.
+# Copyright (C) 2002-2016 by the Free Software Foundation, Inc.
 #
 # This program is free software; you can redistribute it and/or
 # modify it under the terms of the GNU General Public License
@@ -210,6 +210,11 @@ def recast_multipart(msg):
     # If we're left with a multipart message with only one sub-part, recast
     # the message to just the sub-part, but not if the part is message/rfc822
     # because we don't want to lose the headers.
+    # Also, if this is a multipart/signed part, stop now as the original part
+    # may have had a multipart sub-part with only one sub-sub-part, the sig
+    # may still be valid and going further may break it.  (LP: #1551075)
+    if msg.get_content_type() == 'multipart/signed':
+        return
     if msg.is_multipart():
         if (len(msg.get_payload()) == 1 and
                 msg.get_content_type() <> 'message/rfc822'):