Attackers Breach 21,000 Microsoft Exchange Servers, Install Malware Implicating Brian Krebs

Security researcher Brian Krebs wants you to know… “New data suggests someone has compromised more than 21,000 Microsoft Exchange Server email systems worldwide and infected them with malware that invokes both KrebsOnSecurity and Yours Truly by name. Let’s just get this out of the way right now: It wasn’t me.” The Shadowserver Foundation, a nonprofit that helps network owners identify and fix security threats, says it has found 21,248 different Exchange servers which appear to be compromised by a backdoor and communicating with [a domain that begins with brian . krebsonsecurity… Not a safe domain.] Shadowserver has been tracking wave after wave of attacks targeting flaws in Exchange that Microsoft addressed earlier this month in an emergency patch release. The group looks for attacks on Exchange systems using a combination of active Internet scans and “honeypots” — systems left vulnerable to attack so that defenders can study what attackers are doing to the devices and how.

David Watson, a longtime member and director of the Shadowserver Foundation Europe, says his group has been keeping a close eye on hundreds of unique variants of backdoors (a.k.a. “web shells”) that various cybercrime groups worldwide have been using to commandeer any unpatched Exchange servers. These backdoors give an attacker complete, remote control over the Exchange server (including any of the server’s emails)… Shadowserver’s honeypots saw multiple hosts with the Babydraco backdoor doing the same thing: Running a Microsoft Powershell script that fetches the file “krebsonsecurity.exe”… Oddly, none of the several dozen antivirus tools available to scan the file at Virustotal.com currently detect it as malicious. The Krebsonsecurity file also installs a root certificate, modifies the system registry, and tells Windows Defender not to scan the file. Watson said the Krebsonsecurity file will attempt to open up an encrypted connection between the Exchange server and the above-mentioned IP address, and send a small amount of traffic to it each minute.

Shadowserver found more than 21,000 Exchange Server systems that had the Babydraco backdoor installed. But Watson said they don’t know how many of those systems also ran the secondary download from the rogue Krebsonsecurity domain. “Despite the abuse, this is potentially a good opportunity to highlight how vulnerable/compromised MS Exchange servers are being exploited in the wild right now, and hopefully help get the message out to victims that they need to sign up our free daily network reports,” Watson said.