diff --git a/ChangeLog b/ChangeLog
index 125e5b6..95c0d17 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -65,6 +65,13 @@
 
 = mbed TLS 2.16.x branch released xxxx-xx-xx
 
+Security
+   * Fix side channel vulnerability in ECDSA. Our bignum implementation is not
+     constant time/constant trace, so side channel attacks can retrieve the
+     blinded value, factor it (as it is smaller than RSA keys and not guaranteed
+     to have only large prime factors), and then, by brute force, recover the
+     key. Reported by Alejandro Cabrera Aldaya and Billy Brumley.
+
 Bugfix
    * Remove redundant line for getting the bitlen of a bignum, since the variable
      holding the returned value is overwritten a line after.