Fix potential double-free in ssl_set_psk()

Internal ref: IOTSSL-517
diff --git a/ChangeLog b/ChangeLog
index 3ca9268..78664d0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS 1.3.15 released 2015-10-xx
+
+Security
+   * Fix potential double free if ssl_set_psk() is called more than once and
+     some allocation fails. Cannot be forced remotely. Found by Guido Vranken,
+     Intelworks.
+
 = mbed TLS 1.3.14 released 2015-10-06
 
 Security