Tens of thousands of US organizations hit in ongoing Microsoft Exchange hack


A stylized skull and crossbones made out of ones and zeroes.

Tens of thousands of US-based organizations are running Microsoft Exchange servers that have been backdoored by threat actors who are stealing administrator passwords and exploiting critical vulnerabilities in the email and calendaring application, it was widely reported. Microsoft issued emergency patches on Tuesday, but they do nothing to disinfect systems that are already compromised.

KrebsOnSecurity was the first to report the mass hack. Citing multiple unnamed people, reporter Brian Krebs put the number of compromised US organizations at at least 30,000. Worldwide, Krebs said there were at least 100,000 hacked organizations. Other news outlets, also citing unnamed sources, quickly followed with posts reporting the hack had hit tens of thousands of organizations in the US.

Assume compromise

“This is the real deal,” Chris Krebs, the former head of the Cybersecurity and Infrastructure Security Agency, said on Twitter, referring to the attacks on on-premisis Exchange, which is also known as Outlook Web Access. “If your organization runs an OWA server exposed to the internet, assume compromise between 02/26-03/03.” His comments accompanied a Tweet on Thursday from Jake Sullivan, the White House national security advisor to President Biden.

Hafnium has company

Microsoft on Tuesday said on-premises Exchange servers were being hacked in “limited targeted attacks” by a China-based hacking group the software maker is calling Hafnium. Following Friday’s post from Brian Krebs, Microsoft updated its post to say that it was seeing “increased use of these vulnerabilities in attacks targeting unpatched systems by multiple malicious actors beyond HAFNIUM.”

Katie Nickels, director of intelligence at security firm Red Canary, told Ars that her team has found Exchange servers that were…

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