Analysis by: Maria Emreen Viray
ALIASES:

Exploit:ASP/CVE-2021-27065.B!dha (MICROSOFT); Troj/WebShel-O (SOPHOS_LITE)

 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

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

File Size: 2,394 bytes
File Type: ASP
Memory Resident: No
Initial Samples Received Date: 14 Mar 2021

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 encoded JavaScript code in the infected system

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 16.594.07
FIRST VSAPI PATTERN DATE: 14 Mar 2021
VSAPI OPR PATTERN File: 16.595.00
VSAPI OPR PATTERN Date: 15 Mar 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.UWMANO. 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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