Despite (on due to) the release a patch for vulnerable internet-facing email servers, the publicity actually piqued more attention from predators.
In early March, Microsoft released patches for Exchange Server 2013, 2016 and 2019 that will fix a series of pre-authentication remote code execution (RCE) vulnerabilities that allow an attacker to take over any reachable Exchange server, without the need to know any valid account credentials.
The day after the patches’ release, one cybersecurity solutions firm started to observe many more threat actors scanning and compromising Exchange servers en masse. According to Matthieu Faou, who leads ESET’s research effort into the vulnerability chain: “Interestingly, all of them were advanced persistent threat (APT) groups focused on espionage, except one outlier that seemed related to a known coin-mining campaign.”
Faou said it is inevitable that more and more threat actors, including ransomware operators, will have access to the exploits sooner or later. “Our researchers noticed that some APT groups were exploiting the vulnerabilities even before the patches were released. This means we can discard the possibility that those groups built an exploit by reverse engineering Microsoft updates.”
Exchange servers under siege
The firm has discovered that more than 10 different APT groups are exploiting the Microsoft Exchange vulnerabilities to compromise email servers, which includes more than 5,000 email servers that have been affected by malicious activity related to the incident.
The servers belong to organizations (businesses and governments alike) worldwide, including high-profile ones. The threat is not limited to the widely-reported Hafnium group, which installed malware like webshells and backdoors on victims’ email servers. In some cases, several threat actors were targeting the same organization.
The threat groups and behavior clusters identified so far are:
- Tick – compromised the web server of a company based in East Asia that provides IT services. As in the case of LuckyMouse and Calypso, the group likely had access to an exploit prior to the release of the patches.
- LuckyMouse – compromised the email server of a government entity in the Middle East. This APT group likely had an exploit at least one day before the patches were released, when it was still a zero day.
- Calypso – compromised the email servers of government entities in the Middle East and in South America. The group likely had access to the exploit as a zero day. In the following days, Calypso operators targeted additional servers of government entities and private companies in Africa, Asia and Europe.
- Websiic – targeted seven email servers belonging to private companies (in the domains of IT, telecommunications and engineering) in Asia and a governmental body in Eastern Europe. ESET named this new cluster of activity as Websiic.
- Winnti Group – compromised the email servers of an oil company and a construction equipment company in Asia. The group likely had access to an exploit prior to the release of the patches.
- Tonto Team – compromised the email servers of a procurement company and of a consulting company specialized in software development and cybersecurity, both based in Eastern Europe.
- ShadowPad activity – compromised the email servers of a software development company based in Asia and a real estate company based in the Middle East. ESET detected a variant of the ShadowPad backdoor dropped by an unknown group.
- The ‘Opera’ Cobalt Strike – targeted around 650 servers, mostly in the US, Germany, the UK and other European countries just a few hours after the patches were released.
- IIS backdoors – ESET observed IIS backdoors installed via webshells used in these compromises on four email servers located in Asia and South America. One of the backdoors is publicly known as Owlproxy.
- Mikroceen – compromised the exchange server of a utility company in Central Asia, which is the region this group typically targets.
“It is now clearly beyond prime time to patch all Exchange servers as soon as possible. Even those not directly exposed to the internet should be patched. In case of compromise, admins should remove the webshells, change credentials and investigate for any additional malicious activity. The incident is a very good reminder that complex applications such as Microsoft Exchange or SharePoint should not be open to the internet,” Faou said.