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An unpatched zero-day vulnerability in Citrix’s Session Recording Manager allows unauthenticated remote code execution (RCE, paving the way for data theft, lateral movement, and desktop takeover.

According to watchTowr research out today, the issue (which does not yet have a CVE or CVSS score) resides in Citrix's Session Recording Manager, which, as its name implies, records user activity, including keyboard and mouse inputs, websites visited, video streams of desktop activity, and more.

"Citrix advertises the feature as being really useful for monitoring (somewhat obviously), but also for compliance and troubleshooting. It can even be set up so that certain actions (like identifying sensitive data) will trigger recording, which helps meet regulatory needs and flag suspicious activities," the watchTowr researchers noted in the report.

The feature logs session recordings via Microsoft Message Queuing (MSMQ), which enables efficient data transfer from individual computers to centralized storage. However, the Citrix implementation uses BinaryFormatter for serialization and deserialization of the information for easier and more accurate transfer and storage. The utility is unfortunately well-known to be insecure.

BinaryFormatter is a .NET class created by Microsoft, which is in the process of deprecating it: "BinaryFormatter is insecure and can't be made secure. Applications should stop using [it] as soon as possible, even if they believe the data they're processing to be trustworthy," the computing giant said in August.

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On top of the BinaryFormatter issue, Recording Session Manager also involves an exposed MSMQ service that can be reached from any host via HTTP. This, combined with what watchTowr says are misconfigured permissions, paves the way for unauthenticated RCE.

Dark Reading has reached out for comment and planned patching or mitigation information from both watchTowr and Citrix. There is no evidence of in-the-wild exploitation yet, but given Citrix's attractiveness as a cybercrime target, that could soon change.