diff -ru icu.orig/source/common/unistr.cpp icu/source/common/unistr.cpp

--- icu.orig/source/common/unistr.cpp	2019-04-12 00:11:18.000000000 +0200

+++ icu/source/common/unistr.cpp	2020-03-04 18:34:07.225801866 +0100

@@ -1340,7 +1340,10 @@

     if(srcLength == 0) {

       return *this;

     }

-    newLength = oldLength + srcLength;

+    if (uprv_add32_overflow(oldLength, srcLength, &newLength)) {

+      setToBogus();

+      return *this;

+    }

     if(newLength <= getCapacity() && isBufferWritable()) {

       UChar *oldArray = getArrayStart();

       // Do not copy characters when