Analysis by: Maria Emreen Viray
ALIASES:

Exploit:ASP/CVE-2021-27065 (MICROSOFT)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Canal de infección Downloaded from the Internet, Dropped by other malware

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites. It may be hosted on a website and run when a user accesses the said website.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

Tamaño del archivo 2,335 bytes
Tipo de archivo ASP
Residente en memoria No
Fecha de recepción de las muestras iniciales 29 May 2021
Carga útil Others

Arrival Details

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It may be hosted on a website and run when a user accesses the said website.

Backdoor Routine

This Backdoor executes the following commands from a remote malicious user:

  • Execute Arbitrary Commands

Other Details

This Backdoor does the following:

  • It is a modified Microsoft Exchange Offline Address Book (OAB) configuration file
    • ExternalUrl parameter was maliciously altered to directly accept and execute JavaScript code in the infected system

It requires being hosted on a web server in order to proceed with its intended routine.

It takes advantage of the following exploit(s):

  • CVE-2021-26855
  • CVE-2021-26858
  • CVE-2021-27065

  SOLUTION

Motor de exploración mínimo 9.800
Primer archivo de patrones de VSAPI 16.748.05
Primera fecha de publicación de patrones de VSAPI 29 May 2021
Versión de patrones OPR de VSAPI 16.749.00
Fecha de publicación de patrones OPR de VSAPI 30 May 2021

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 users must disable System Restore to allow full scanning of their computers.

Step 2

Scan your computer with your Trend Micro product to delete files detected as Backdoor.ASP.WEBSHELL.UWMAOM. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check the following Trend Micro Support pages for more information:


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