Researcher warns of new zero-day in Microsoft Exchange under exploit


Reports are emerging that a new zero-day exists in Microsoft Exchange and is being exploited in the wild, a well-known security researcher has warned.

Kevin Beaumont said in a series of tweets that he could confirm that a significant number of Exchange servers had been hijacked, including a honeypot.

He added that while Microsoft appeared to be aware of the new vulnerability, the company had yet to notify customers.

Beaumont pointed out a publication by a Vietnamese source named GTSC Cyber ​​Security Company who said details of the vulnerability, noticed in August, were sent to Zero-Day Initiative who checked and acknowledged two bugs.

“However, so far GTSC has seen other customers also experience the same issue,” the report said. “After careful testing, we have confirmed that these systems were attacked using this 0-day vulnerability.

“To help the community temporarily stop the attack before an official patch from Microsoft is available, we are posting this article for organizations that use the Microsoft Exchange messaging system.”

iTWire has contacted Microsoft for its opinion on the matter.

The new vulnerability appears to resemble the ProxyShell default for which Microsoft has released updates in May and July Last year.

Beaumont pointed to a portion of the GTSC report that said, “While providing SOC service to a customer, GTSC Blueteam detected exploit requests in IIS logs with the same format as the ProxyShell vulnerability: autodiscover/autodiscover.json?[email protected]

“Checking other logs as well, we saw that the attacker can run commands on the attacked system. The version number of these Exchange servers showed that the latest update had already been installed, so an exploit using Proxyshell vulnerability was impossible -> Blueteam analysts can confirm this was a new 0-day RCE vulnerability.

“This information was sent to Redteam, and Redteam members of GTSC conducted research to answer these questions: Why were the exploit requests similar to the ProxyShell bug? How is the RCE implemented?

“GTSC Redteam managed to figure out how to use the above path to access a component in the Exchange backend and perform RCE. However, at this time, we would like to NOT publish the technical details of the vulnerability at this time.”

Beaumont added that it’s not unusual for a significant number of Exchange servers to be backdoored because the patching process was such a mess, with people ending up on old updates. of content and not properly fixing ProxyShell.

“I guess there might be an additional vulnerability, but from the blog it looks like they are hitting it via ProxyShell, an old vulnerability (for which MS didn’t push the IIS rewrite module ),” he wrote.

“I suspect it may be a new _exploit_ rather than vulnerabilities, time will tell.

“Public ProxyShell exploits are terrible – for example, they hard-code knowing server names, email boxes, etc. – you can actually exploit them without those details.”


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