As few weeks back, we sent a notice to the ProtonMail community regarding the DDoS attacks that we have been facing. Today we would like to provide a brief update of the situation.

Starting on June 27th, ProtonMail started to be hit by sustained DDoS attacks.

The attack campaign continues to this day, but there has been little to no user impact.

Thus far the attacks have included: Rapidly morphing DDoS attacks with the combination of SYN floods, TCP handshake violations (first packets are not SYNs), IPv4 TCP SYN floods, TCP Zero Sequence, ACK Floods, NTP nonstandard port floods, and reflection attacks on SSDP, NTP, Chargen, LDAP and Memcache protocols. Pulsed/Burst DDoS attacks, with multiple attack vectors and rapid changes within minutes. Attacks up to 25Gbs in volume. This attack was largely challenging to handle because of its complexity, not the size/volume. No unknown attack vectors were used, but they were rapidly changing, and hence the complexity.



Since November 2015, ProtonMail has been protected by Radware’s Cloud DDoS Protection Services, and in this instance, Radware was able to successfully mitigate nearly all of these attacks. However, due to the nature of the ferocity and attack ingenuity, some of the attacks were only partially mitigated and briefly resulted in some service outages at the outset of the campaign.

In order to improve mitigation performance, Radware immediately upgraded their scrubbing centers and processes to provide better protection against rapidly changing attacks. As a result, attack mitigation through the upgraded Radware scrubbing center has been successful in the past couple weeks.

After the upgrade, we have found that Radware’s technology actually works well against rapidly evolving attacks, and the automatic mitigation capabilities are essential for reducing the response times when coming under attack frequently. We also deeply appreciate the support that we have received from the team at Radware, and the fact that they made defending ProtonMail a priority. Going forward, we plan to utilize a multi-layered DDoS defense strategy and will continue to partner with Radware on the first line of defense.

We appreciate your patience through these attacks and look forward continuing to provide you with secure and private email services.

Best Regards,

The ProtonMail Team