1 files changed, 7 insertions, 3 deletions
diff --git a/Swiften/IDN/LibIDNConverter.cpp b/Swiften/IDN/LibIDNConverter.cpp
index 0c01352..e2a87be 100644
--- a/Swiften/IDN/LibIDNConverter.cpp
+++ b/Swiften/IDN/LibIDNConverter.cpp
@@ -1,3 +1,3 @@
 /*
- * Copyright (c) 2012-2016 Isode Limited.
+ * Copyright (c) 2012-2018 Isode Limited.
  * All rights reserved.
@@ -26,3 +26,3 @@ using namespace Swift;
 namespace {
-    static const int MAX_STRINGPREP_SIZE = 1024;
+    static const size_t MAX_STRINGPREP_SIZE = 1024;
 
@@ -46,3 +46,4 @@ namespace {
 
-        input.resize(MAX_STRINGPREP_SIZE);
+        // Ensure we have enough space for stringprepping, and that input is always NUL terminated
+        input.resize(std::max(MAX_STRINGPREP_SIZE, input.size() + 1));
         if (stringprep(&input[0], MAX_STRINGPREP_SIZE, static_cast<Stringprep_profile_flags>(0), getLibIDNProfile(profile)) == 0) {
@@ -79,2 +80,5 @@ boost::optional<std::string> LibIDNConverter::getIDNAEncoded(const std::string&
         free(output);
+        if (result.size() > 255) {
+            return boost::optional<std::string>();
+        }
         return result;