Pierluigi Paganini March 09, 2020

Multiple state-sponsored hacking groups are attempting to exploit a vulnerability recently addressed in Microsoft Exchange email servers.

Cybersecurity firm Volexity is warning that nation-state actors are attempting to exploit a vulnerability recently addressed in Microsoft Exchange email servers tracked as CVE-2020-0688.

The experts did not provide details on the threat actors that are exploiting the vulnerability, according ZDNet that cited a DOD source the attackers belong to prominent APT groups.

The CVE-2020-0688 flaw resides in the Exchange Control Panel (ECP) component, the root cause of the problem is that Exchange servers fail to properly create unique keys at install time.

“Knowledge of a the validation key allows an authenticated user with a mailbox to pass arbitrary objects to be deserialized by the web application, which runs as SYSTEM.” reads the advisory published by Microsoft.

A remote, authenticated attacker could exploit the CVE-2020-0688 vulnerability to execute arbitrary code with SYSTEM privileges on a server and take full control.

Security experts Simon Zuckerbraun from Zero Day Initiative published technical details on how to exploit the Microsoft Exchange CVE-2020-0688 along with a video PoC.

“Similarly, any outside attacker who compromised the device or credentials of any enterprise user would be able to proceed to take over the Exchange server. Having accomplished this, an attacker would be positioned to divulge or falsify corporate email communications at will.” wrote Zuckerbraun. “Accordingly, if you’re an Exchange Server administrator, you should treat this as a Critical-rated patch and deploy it as soon as your testing is complete. Microsoft lists this with an Exploit Index of 1, which means they expect to see exploits within 30 days of the patch release.”

A couple of weeks ago, the popular security researcher Kevin Beaumont reported mass scanning for the CVE-2020-0688 (Microsoft Exchange 2007+ RCE vulnerability).

In the same period, experts at Bad Packets confirmed an ongoing scanning activity.

Microsoft released security updates for the CVE-2020-0688 flaw on February 11, at the time experts urged administrators to patch their servers before attackers could reach them and exploit the issue.

Since the disclosure of the flaw, at least three of proof-of-concept exploit codes were released online [1, 2, 3] and nation-state actors started using them in the wild.

APT groups are interested in hacking Microsoft exchange servers to intercept and read the company’s email traffic.

“Volexity has observed multiple APT actors exploiting or attempting to exploit on-premise Exchange servers. In some cases the attackers appear to have been waiting for an opportunity to strike with credentials that had otherwise been of no use.” reads the analysis published by Volexity. “Volexity has also observed multiple concerted efforts by APT groups to brute-force credentials by leveraging Exchange Web Services (EWS) in an effort to likely exploit this vulnerability. While brute-forcing credentials is a common occurrence, the frequency and intensity of attacks at certain organizations has increased dramatically following the vulnerability disclosure.”

The good news is that the CVE-2020-0688 Exchange vulnerability is not easy to exploit because the attackers first need to be authenticated to the target system then run malware to trigger the issue and hijack the victim’s email server.

Pierluigi Paganini

(SecurityAffairs – hacking, CVE-2020-0688)

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