How Burp Bambdas Revolutionize Vulnerability Hunting with Custom Hash Detection

In a recent client engagement, Kulkan Security's penetration testing team stumbled upon a critical vulnerability: attackers could exploit predictable hash values in HTTP requests to hijack user accounts. This discovery wasn't just another bug—it highlighted a systemic gap in manual security reviews. As Nahuel D. Sanchez, Security Consultant Manager at Kulkan, recounts, the team realized they needed a way to automate the hunt for similar flaws. Enter Burp Bambdas: lightweight Java scripts that integrate with Burp Suite to filter, analyze, and modify web traffic on the fly.

The Power of Bambdas in Cybersecurity

Burp Bambdas, part of PortSwigger's Montoya API, allow security professionals to write custom logic for real-time HTTP inspection. Unlike static filters, Bambdas can compute values dynamically—making them ideal for detecting elusive threats like hardcoded hashes. In this case, Kulkan's team developed a Bambda that calculates SHA-256 hashes of sensitive data (e.g., emails or usernames) and scans responses for matches. Here’s the core Java snippet that powers it:

if (!requestResponse.hasResponse()) { return false; }
String email = "[email protected]";
ByteArray emailHash = utilities().cryptoUtils().generateDigest(
    ByteArray.byteArray(email), DigestAlgorithm.SHA_256);
String emailHashAsString = HexFormat.of().formatHex(emailHash.getBytes());
if (requestResponse.response().contains(emailHashAsString, false)) { 
    return true;
}
return false;

This code, adaptable to any hash algorithm or input value, flags requests containing targeted hashes—turning hours of manual review into a one-click audit. Sanchez emphasizes its flexibility: "Change the hashing algorithm or source data in seconds. It’s like having a bespoke vulnerability radar."

Why This Matters for Developers and Pentesters

Predictable hashes are a silent killer in web security, often enabling privilege escalation or data leaks. Tools like this Bambda shift the focus from reactive patching to proactive discovery, especially in complex multi-step attacks. For engineering teams, it underscores the value of extending Burp Suite beyond out-of-the-box features—using Montoya API’s utilities for hashing, logging, and byte manipulation to build custom safeguards. As Sanchez notes, this approach isn’t just about finding bugs; it’s about refining the pentester’s workflow to catch what automated scanners miss.

In an era where speed is critical, Bambdas exemplify how micro-automations can yield macro wins. Kulkan’s experiment is a call to action: don’t just use tools—reshape them. And with Burp’s growing ecosystem, the next quick win might be a few lines of code away.

Source: Adapted from the original article by Nahuel D. Sanchez on Kulkan Security's blog.