Solve Hack the Box and other CTF challenges with Snyk

Hack The Box is a gamified cybersecurity training platform that uses hands-on capture-the-flag exercises involving vulnerable virtual machines and smaller challenges to teach offensive security skills. Using the BlinkerFluids web challenge as an example, the account examines a Node.js invoice application that converts user-supplied Markdown into PDFs and provides its full source code as downloadable challenge material. Static analysis with the Snyk CLI identified several issues, including CSRF, information exposure, denial-of-service risks, and DOM-based XSS, but none appeared useful for retrieving the target flag. A software composition analysis of the application’s dependencies then identified a critical remote code execution vulnerability in version 4.1.0 of the md-to-pdf package, caused by its use of the gray-matter library’s JavaScript-capable front-matter parsing. By submitting crafted Markdown that executed JavaScript to read the protected flag file and embed its contents in a generated PDF, the challenge could be completed. The example illustrates how dependency scanning can help attackers identify exploitable flaws quickly while also giving developers remediation guidance, such as upgrading md-to-pdf to a fixed version.

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