Meris first got our attention due to an exceptionally large 17.2 million requests per second (rps) DDoS attack that it launched against one of our customers. This attack, along with subsequent attacks originated by the Meris botnet, was automatically detected and mitigated by our DDoS protection systems. Cloudflare customers, even ones on the free plan, are protected against Meris attacks.

Over the past months, we've been tracking and analyzing the activity of the Meris botnet. Some of the main highlights include:

• Meris targets approximately 50 different websites every single day with a daily average of 104 unique DDoS attacks.
• More than 33% of all Meris DDoS attack traffic targeted China-based websites.
• More than 12% of all websites that were attacked by Meris are operated by US-based companies.

So what is Meris?

Meris (Latvian for plague) is the name of an active botnet behind a series of recent DDoS attacks that have targeted thousands of websites around the world. It was originally detected in late June 2021 by QRator in joint research they conducted with Yandex. Their initial research identified 30,000 to 56,000 bots, but they estimated that the numbers are actually much higher, in the ballpark of 250,000 bots.

The Meris botnet is formed of infected routers and networking hardware manufactured by the Latvian company MikroTik. According to MikroTik's blog, the attackers exploited a vulnerability in the router's operating system (RouterOS) which enabled attackers to gain unauthenticated remote access to read and write arbitrary files (CVE-2018-14847).

RouterOS is the router operating system that's used by MikroTik's routers and the RouterBOARD hardware product family, which can also be used to turn any PC into a router. Administration of RouterOS can be done either via direct SSH connection or by using a configuration utility called WinBox. The vulnerability itself was possible due to a directory traversal vulnerability in the WinBox interface with RouterOS.

Directory traversal is a type of exploit that allows attackers to travel to the parent directories to gain access to the operating system's file system, a method and structure of how data is stored and retrieved in the operating system. Once they gain access to the file system, attackers can then read the existing files that administer the router and write files directly into the file system to administer the routers to their botnet needs.

While the vulnerability was patched after its detection back in 2018, it's still being exploited in compromised devices that do not use the patched RouterOS versions, or that use the default usernames and passwords. MicroTik has advised its customers to upgrade their devices' OS version, to only allow access to the devices via secure IPsec, and to inspect for any abnormalities such as unknown SOCKS proxy settings and scripts.

To launch volumetric attacks, the botnet uses HTTP pipelining which allows it to send multiple requests over a single connection, thus increasing its total attack throughput. Furthermore, in an attempt to obfuscate the attack source, the botnet uses open SOCKS proxies to proxy their attack traffic to the target.

Cloudflare's DDoS protection systems automatically detect and mitigate Meris attacks. One of the mitigation actions that the system can choose to use is the 'Connection Close' action which eliminates the risk of HTTP pipelining and helps slow down attackers. Additionally, as part of Cloudflare's threat intelligence suite, we provide a Managed IP List of Open SOCKS Proxies that customers can use as part of their firewall rules --- to block, challenge or rate-limit traffic that arrives via SOCKS proxies.

How does Meris compare to Mirai?

About five years ago, Mirai (Japanese for future) - the infamous botnet that infected hundreds of thousands of IoT devices - launched record-breaking DDoS attacks against websites.

There have been many variants of the Mirai botnet since its source code was leaked. One version of Mirai, called Moobot, was detected last year when it attacked a Cloudflare customer with a 654 Gbps DDoS attack. Another variant recently made a resurgence when it targeted Cloudflare customers with over a dozen UDP and TCP based DDoS attacks that peaked multiple times above 1 Tbps, with a max peak of approximately 1.2 Tbps.

While Mirai infected IoT devices with low computational power, Meris is a swarm of routers that have significantly higher processing power and data transfer capabilities than IoT devices, making them much more potent in causing harm at a larger scale to web properties that are not protected by sophisticated cloud-based DDoS mitigation.

Tracking the Meris botnet attacks

Since the appearance of Meris, Cloudflare’s systems automatically detected and mitigated Meris attacks using the existing mitigation rules. During our analysis of the Meris botnet attacks, our security experts noticed the attack vectors adapt to try and bypass Cloudflare’s defenses. Needless to say, they were not successful. But we wanted to stay many steps ahead of attackers — and so our engineers deployed additional rules that mitigate Meris attacks even more comprehensively. A side effect of these mitigation rules is that it also provides us with more granular threat intelligence on the Meris attacks.

Since we deployed the new rules in early August, we’ve seen Meris launch an average of 104 DDoS attacks on Cloudflare customers every day. The highest figure we’ve seen was on September 6, when Meris was used to launch 261 unique attacks against Cloudflare customers.

During that same day, on September 6, attacks from Meris accounted for a record-breaking 17.5% of all L7 DDoS attacks that Cloudflare observed.

Overall, Meris targets about 50 different websites and applications every single day. Although the average attack peaked at 106K rps, the median attack size was actually smaller at 17.6K rps. The largest attack we’ve seen was 17.2M rps and that occurred in July. In the graph below, you can see the daily highest requests per second rate after we deployed the new rules. Since then, the largest attack we’ve seen was 16.7M rps, which took place on August 19.

Meris used to target Banks, Financial Services, and Insurance companies

Over the past few months, the industry that received the most attack traffic from the Meris botnet was the Banking, Financial Services, and Insurance (BFSI) industry.

Following the BFSI industry, the most attacked industries were the Publishing, Gaming/Gambling, and IT Services industries. And while BFSI was the number one most attacked industry when considering the Meris DDoS activity rate, it only came in fourth place when considering the percentage of targeted websites.

In terms of the percentage of targeted websites, the Computer Software industry came in first place. Almost 4% of all impacted websites were of Computer Software companies protected by Cloudflare, followed by Gaming/Gambling and IT Services with 3% and 2%, respectively.

Attacks on industries over time

Besides the total breakdowns shown above, we can also view the top industries the botnet attacked over time to understand the changing trends. These trends may be tied to political events, new video game releases, sporting events, or any other global or local public interest events.

Off the top, we can already see the two largest peaks on August 9 and August 29 — mainly on the Computer Software, Gaming/Gambling, and IT industries. Another interesting peak occurred on August 14 against Cryptocurrency providers.

In late August, the botnet was pointed against gambling and casino websites, generating attacks at rates of hundreds of thousands to millions of requests per second. A second significant wave against the same industry was launched in early September.

Meris targets websites in China, Australia, and US

Similarly to the analysis of the top industries, we can calculate the Meris DDoS activity rate per target country to identify which countries came under the most attacks. In total, China-based companies saw the largest amount of DDoS attacks. More than 33% of all requests generated by Meris were destined for China-based companies that are protected by Cloudflare. Australia came in second place, and the US in third.

On the other hand, when we look at the number of websites that were targeted by Meris, the US came in first place. More than 12% of all websites that were targeted by Meris are operated by US-based companies. China came in second place with 5.6% and Russia in third with 4.4%.

Attacks on countries over time

Over time, we can see how the attacks on the top countries change. Similarly to the per-industry breakdown, we can also see two large peaks. The first one occurred on the same spike as the per-industry breakdown on August 9. However, the second one here occurred on September 1.

Location of the Meris bots

Although only tens of thousands of bots have been detected per attack, it is estimated that there are roughly 250,000 bots worldwide. As indicated above, the botnet is formed of MikroTik routers. Using the source IP address of the routers, we’re able to identify the origin country of the bots to paint a geographical representation of the bots' presence and growth over time.

The change in the location of the bots doesn’t necessarily indicate that the botnet is growing or shrinking. It could also be that different bot groups are activated from time to time to spread the load of the attacks while attempting not to get caught.

At the beginning of August, the majority of the bots were located in Brazil. But by the end of August, that number plummeted to a single digit percentage close to zero. Meanwhile, the number of infected devices grew in the United States. From the beginning of September, the number of bots was significantly higher in the US, Russia, India, Indonesia, and China.

Cloudflare protects against Meris attacks

Cloudflare operates autonomous DDoS protection systems that automatically detect and mitigate DDoS attacks of all types, including attacks launched by Meris and Mirai. These systems are also customizable, and Cloudflare customers can tweak and tune their DDoS protection settings as needed with the HTTP DDoS Managed Ruleset and the L3/4 DDoS Managed Ruleset.