Guided Pentest: Web (Task 6 - File Upload Security Assessment)

Completed the file upload security assessment phase of the Guided Pentest: Web room.

Objective

Evaluate the security controls implemented within the application's file upload functionality and identify potential weaknesses that could be abused by an attacker.

Skills Practised
File upload vulnerability assessment
Input validation analysis
Web application security testing
Attack surface identification
Security control evaluation
Secure file handling review
Key Activities
Analysed the application's file upload mechanism.
Examined how uploaded files were validated before being accepted by the server.
Investigated client-side and server-side filtering controls.
Reviewed file extension validation methods.
Assessed file type verification processes and MIME type handling.
Evaluated the effectiveness of upload restrictions designed to prevent malicious file uploads.
Findings
Upload Validation Controls

The application relied on several validation mechanisms intended to prevent unauthorised file uploads, including:

File extension validation
File type (MIME type) validation
Content verification checks
File naming restrictions
Security Considerations

File upload functionality presents a significant attack surface when validation controls are improperly implemented. Attackers may attempt to bypass filtering mechanisms through alternative file extensions, manipulated content types, or crafted payloads.

Potential Impact

Weak upload validation can allow attackers to:

Upload unauthorised files
Execute malicious code on the server
Gain remote access to the application environment
Escalate privileges through chained vulnerabilities
Compromise the confidentiality, integrity, and availability of hosted systems
Lessons Learned

Secure file upload implementations require multiple layers of validation rather than relying on a single control. Client-side checks should never be trusted as a security boundary, and all validation must be enforced server-side. Effective protection typically combines extension whitelisting, MIME type verification, content inspection, file renaming, and storage outside executable directories.

Security Principles Reinforced
Defence in Depth
Secure Input Validation
Least Privilege
Server-Side Trust Boundaries
Secure File Handling
Outcome

Successfully analysed the application's upload validation mechanisms and identified areas that could be targeted in subsequent phases of the penetration test to achieve more significant impact.
Link to the room: https://tryhackme.com/room/guidedpentestweb?taskNo=6&sharerId=64748eabb4eb8f1638e47a22