Fix potential integer overflow parsing DER CRT

This patch prevents a potential signed integer overflow during the
certificate version verification checks.
diff --git a/ChangeLog b/ChangeLog
index e50604d..e847b65 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -17,6 +17,9 @@
      encoded X509 CRLs. The overflow would enable maliciously constructed CRLs
      to bypass the version verification check. Found by Peng Li/Yueh-Hsun Lin,
      KNOX Security, Samsung Research America
+   * Fix a potential integer overflow in the version verification for DER
+     encoded X509 certificates. The overflow would enable maliciously
+     constructed certificates to bypass the certificate verification check.
 
 = mbed TLS 1.3.20 branch released 2017-06-21