"🛡️ Mitigation Tips Against Stealthy VBA Macros 📝"**
To protect against these stealthy VBA macros, consider disabling macros in Microsoft Office and restricting execution to trusted sources. 🚫📄
Educate users about the risks associated with enabling macros and employ robust email gateways for scanning attachments. 🎓📧
A YARA rule is also available to flag potential threats without relying on PDF header checks. 🚩🔍
key points:
Malicious Word Document in a PDF-like Header: The malicious Word document is concealed within a PDF-like header that contains the signature %PDF-1.7, typically associated with PDF files.
MIME Encapsulation of HTML Documents: Within the fake PDF structure, there is a MIME encapsulation of aggregate HTML documents (MHTML Web Archive) that contains an embedded Base64 encoded ActiveMIME object. ActiveMIME is an undocumented Microsoft file format often used to store VBA Macros.
Obfuscation Techniques: Various obfuscation techniques are employed to evade detection based on signatures. These include the use of a non-compliant MIME type, fragmentation of Base64 encoded strings, and URL percent-encoded strings to obscure links.
PDF Header Not Required: Interestingly, the embedded MHT document file doesn't actually require a PDF header. Any text preceding the MHT file allows Microsoft Word to open the document file and execute the malicious macro if enabled.
Evasion of Signature-Based Detection: This technique can evade signature-based detection systems that specifically scan for a PDF header. The analysis shows a significant difference in detection rates between samples with and without the fake PDF header.
Mitigation Advice: To protect users from such threats, the summary provides several mitigation recommendations, including configuring Microsoft Office to disable macros by default, restricting macro execution to trusted sources, educating users about macro risks, and using robust email gateways for scanning attachments.
YARA Rule: A YARA rule is provided to identify potential malicious macros embedded in files without conducting PDF header checking. This rule checks for specific strings and patterns within files to flag potential threats.
Source: Trustwave SpiderLabs Blog
Tags: #Cybersecurity #Mitigation #UserEducation #YARARule #Trustwave #SpiderLabs #EmailSecurity 🌐🔐🛡️
⚯ Michel de Cryptadamus ⚯
vPierre
🛡 H3lium@infosec.exchange/:~# 
