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Common services, for example Outlook on the web (formerly known as Outlook Web App or OWA) or Exchange admin center (EAC formerly known as the Exchange Control Panel or ECP), executing net.exe, cmd.exe, and other known living-off-the-land binaries ( LOLBins) like mshta.exe is very suspicious and should be further investigated.įigure 1. Whenever attackers interacted with the web shell, the hijacked application pool ran the command on behalf of the attacker, generating an interesting process chain. The telemetry showed attackers operating on on-premises Exchange servers using deployed web shells. In April, multiple Exchange-specific behavior-based detections picked up unusual activity. suspicious activities in Exchange servers.
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These detection engines are powered by cloud-based machine learning classifiers that are trained by expert-driven profiling of legitimate vs. A more durable approach to detecting web shell activity involves profiling process activities originating from external-facing Exchange applications.īehavior-based blocking and containment capabilities in Microsoft Defender ATP, which use engines that specialize in detecting threats by analyzing behavior, surface suspicious and malicious activities on Exchange servers.
#Zero z server attack code#
Behavior-based detection and blocking of malicious activities on Exchange serversĪdversaries like using web shells, which are relatively small pieces of malicious code written in common programming languages, because these can be easily modified to evade traditional file-based protections. As we discussed in a previous blog, web shells allow attackers to steal data or perform malicious actions for further compromise. In many cases, after attackers gain access to an Exchange server, what follows is the deployment of web shell into one of the many web accessible paths on the server.
#Zero z server attack update#
The security update that fixes this vulnerability has been available for several months, but, notably, to this day, attackers find vulnerable servers to target. The first scenario is more common, but we’re seeing a rise in attacks of the second variety specifically, attacks that exploit Exchange vulnerabilities like CVE-2020-0688.
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This is an attacker’s dream: directly landing on a server and, if the server has misconfigured access levels, gain system privileges. The second scenario is where attackers exploit a remote code execution vulnerability affecting the underlying Internet Information Service (IIS) component of a target Exchange server.
#Zero z server attack download#
The first and more common scenario is attackers launching social engineering or drive-by download attacks targeting endpoints, where they steal credentials and move laterally to other endpoints in a progressive dump-escalate-move method until they gain access to an Exchange server. There are two primary ways in which Exchange servers are compromised. Attackers know this, and they leverage this knowledge to gain a stable foothold on a target organization. This is exacerbated by the fact that Exchange servers have traditionally lacked antivirus solutions, network protection, the latest security updates, and proper security configuration, often intentionally, due to the misguided notion that these protections interfere with normal Exchange functions. If compromised, Exchange servers provide a unique environment that could allow attackers to perform various tasks using the same built-in tools or scripts that admins use for maintenance. Any threat or vulnerability impacting Exchange servers should be treated with the highest priority because these servers contain critical business data, as well as highly privileged accounts that attackers attempt to compromise to gain admin rights to the server and, consequently, complete control of the network. Securing Exchange servers is one of the most important things defenders can do to limit organizational exposure to attacks.