Datashield recommends patching any Microsoft Exchange servers due to the recently released series of vulnerabilities, CVE-2021-26855 in particular, and the evidence of this exploit being utilized in the wild. An unauthenticated attacker can compromise the server and obtain access into the network. There is no current mitigation besides patching the affected Exchange servers. Datashield has deployed some initial detections for this CVE, but is still evaluating and creating new detections as we gather more information.
- Microsoft Exchange Server 2013
- Microsoft Exchange Server 2016
- Microsoft Exchange Server 2019
Datashield also recommends performing the following the steps to determine if there was any compromise on the Exchange servers:
- Analyzing Exchange HttpPRoxy logs
- Analyzing Exchange log files
- Analyzing Windows Application event logs
- Checking for evidence of webshells
- Checking for evidence of LSASS dumps
Further details are outlined in the Microsoft blog (first link below) for performing the above outlined steps. If you need any assistance or have any questions regarding searching for these IOCs, please reach out to the MSSDS and we will answer any questions that you have. If you utilize Defender for endpoint or Azure Sentinel, there are also several queries your teams can run in those environments. We are in the process of proactively scanning and hunting if we have access to any of the above logs or technologies.
If you have any questions regarding this vulnerability, please contact us.