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Friday, 30 September 2022 08:31

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

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

Reports are emerging that a new zero-day exists in Microsoft Exchange and that it 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 significant numbers of Exchange servers had been backdoored, including a honeypot. UPDATE

He added that while Microsoft appeared to be aware of the new vulnerability, the company had not yet informed its customers.

Beaumont pointed to a post by a Vietnamese source named GTSC Cyber Security Company that said details of the vulnerability, noticed in August, had been sent to the Zero-Day Initiative which had verified and acknowledged two bugs.

"However up to now, GTSC has seen other customers also experiencing the similar problem," the report said. "After careful testing, we confirmed that those systems were being attacked using this 0-day vulnerability.

"To help the community temporarily stop the attack before an official patch from Microsoft is available, we publish this article aiming to those organisations who are using Microsoft Exchange email system."

iTWire has contacted Microsoft for its take on the issue.

The new vulnerability appears to resemble the ProxyShell flaw for which Microsoft issued updates in May and July last year.

Beaumont pointed to one part of the GTSC report which said: "While providing SOC service to a customer, GTSC Blueteam detected exploit requests in IIS logs with the same format as ProxyShell vulnerability: autodiscover/autodiscover.json? @<Exchange-backend-endpoint>&Email=autodiscover/autodiscover.json%3f @

"Also checking other logs, we saw that the attacker can execute commands on the attacked system. The version number of these Exchange servers showed that the latest update had already installed, so an exploitation using Proxyshell vulnerability was impossible -> Blueteam analysts can confirm that it was a new 0-day RCE vulnerability.

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

"GTSC Redteam successfully figured 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 NOT to release technical details of the vulnerability yet."

Beaumont added that it was not unusual for a significant number of Exchange servers to be backdoored, since the patching process was such a mess, with people ending up on old Content Updates and not patching ProxyShell properly.

"I guess there may be an additional vuln in there, but from the blog it looks like they're reaching it via ProxyShell, an old vuln (that MS didn't push IIS rewrite module for)," he wrote.

"I guess it may be a new _exploit_ rather than vulnerabilities, time will tell.

"The public ProxyShell exploits are terrible – e.g. they hardcode knowing server names, email mailboxes etc - you can in fact exploit without those details."

Contacted for comment, Satnam Narang, senior staff research engineer with security firm Tenable, told iTWire that at this point, Microsoft had not yet confirmed the vulnerability.

“There is an unconfirmed report that a zero-day vulnerability in Microsoft Exchange Server has been exploited in the wild since early August," Narang said. The report comes from researchers at GTSC Cybersecurity Technology Company Limited, who say they have reported their findings to Microsoft via the Zero Day Initiative (ZDI).

“At this point, Microsoft has not yet confirmed the report. What we do know is that the researchers say this bears similarities to the ProxyShell vulnerabilities that were disclosed last year, which continue to be exploited in the wild by attackers along with ProxyLogon, a set of vulnerabilities that were initially disclosed in early 2021.

“It is clear that determined attackers are continuing to find success targeting vulnerable Exchange Server instances using ProxyLogon and ProxyShell despite the availability of patches for well over a year now.

"In fact, in its recent joint advisory with various security agencies around the world regarding Iranian IRGC-affiliated attacks, the Australian Cyber Security Centre (ACSC) noted that attackers have leveraged ProxyShell to gain access to Australian organisations.

“Organisations should prioritise patching their on-premise Exchange Server instances if they have not done so yet and should, out of an abundance of caution, look for signs of compromise in the form of Web shells being placed on their Exchange Server instances, as the web shells are a way for attackers to maintain persistence.

"If it is confirmed to be a valid zero-day and Microsoft does issue patches, we strongly encourage all Australian organisations to ensure they apply the latest set of patches to prevent future exploitation of new flaws within Exchange Server.”

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Sam Varghese

Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.

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