Fix NullPointerException when Host header is lowercase

[63n0]

Summary

Param Miner currently only recognizes the Host header when it is written as Host: .

When running Guess Headers against an HTTP/1.1 request that uses a lowercase host header, the host value is not extracted correctly, which later results in a NullPointerException.

This change makes the Host header lookup case-insensitive so that requests using host: are handled correctly.

Reproduction

Run Guess Headers against the following request:

GET / HTTP/1.1
host: localhost

The extension throws the following exception:

java.lang.NullPointerException: Cannot invoke "java.lang.CharSequence.toString()" because "replacement" is null
	at java.base/java.lang.String.replace(String.java:3151)
	at burp.ParamNameInsertionPoint.getValue(BurpExtender.java:341)
    ...

Root Cause

The code only checks for headers beginning with Host: :

if (header.startsWith("Host: ")) {

HTTP header field names are case-insensitive, so requests using host: are not recognized. As a result, the host variable remains unset and a NullPointerException occurs later during header guessing.

Fix

Perform a case-insensitive match when extracting the Host header value.