Categories: US-Cert-Repository

Webshells Observed in Post-Compromised Exchange Servers



Original release date: March 25, 2021

CISA has added two new Malware Analysis Reports (MARs) to Alert AA21-062A: Mitigate Microsoft Exchange Server Vulnerabilities. Each new MAR (AR21-084A and AR21-084B) identifies a webshell observed in post-compromised Microsoft Exchange Servers. After successful exploiting a Microsoft Exchange Server vulnerability for initial accesses, a malicious cyber actor can upload a webshell to enable remote administration of the affected system.

CISA has also updated seven previously released MARs. The updated MARs now include CISA-developed YARA rules to help network defenders detect associated malware.

CISA encourages users and administrators to review the following resources for more information:

  • CISA Alert AA21-062A: Mitigate Microsoft Exchange Server Vulnerabilities
  • MAR-10328877-1.v1: China Chopper Webshell
  • MAR-10328923-1.v1: China Chopper Webshell
  • MAR-10329107-1.v1: China Chopper Webshell
  • MAR-10329297-1.v1: China Chopper Webshell
  • MAR-10329298-1.v1: China Chopper Webshell
  • MAR-10329301-1.v1: China Chopper Webshell
  • MAR-10329494-1.v1: China Chopper Webshell
  • MAR-10329499-1.v1: China Chopper Webshell
  • MAR-10329496-1.v1: China Chopper Webshell
  • CISA web page Remediating Microsoft Exchange Vulnerabilities
  • CISA web page Ransomware Guidance and Resources

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