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Configuring the Logger capture filter with Bambdas

• Last updated: February 13, 2025

• Read time: 3 Minutes

You can apply Java-based Bambdas to create custom capture filters for Logger. You can do this in two ways:

• Load existing Bambdas - Load Bambdas from your Bambda library.

• Create new Bambdas - Write Bambdas directly in the Bambda mode tab.

Keyboard shortcuts

To speed up your workflow when creating or loading Bambdas, you can use the following keyboard shortcuts:

• Save - Ctrl + S or Cmd + S

• Save as - Ctrl + Shift + S or Cmd + Shift + S

• Create new Bambda - Ctrl + N or Cmd + N

• Load recent Bambda - Ctrl + O or Cmd + O

Loading Bambdas from your library

You can load and apply Bambdas that are stored in your library to filter which types of items Logger captures.

To load a Bambda from your library:

1. In the Logger tab, click the filter bar to open the Logger capture filter window.

2. In the Logger capture filter window, click Bambda mode.

3. Click Load.

4. Select a recent Bambda from the list.

5. [Optional] If required, edit the Bambda:

   1. Make your changes.

   2. Click Apply to compile and test the Bambda. Fix any errors shown in the Compilation errors panel. For more information, see Troubleshooting Bambdas.

   3. Save your changes:

      • To overwrite the existing Bambda, click Save > Save.

      • To save a new version, click Save > Save as.

6. Click Apply & close.

Burp compiles your Bambda and applies it to any future traffic generated in this project.

Creating custom Bambdas

You can write your own Bambdas directly in the Bambda mode tab.

Converting filter settings to Bambdas

You can convert filter settings to a Bambda as a starting point for further customization:

1. In the Logger tab, click the filter bar to open the Logger capture filter window.

2. Make changes to the filter settings as necessary.

3. At the bottom of the Logger capture filter window, click Convert to Bambda.

Your filter is converted into a Bambda, enabling you to customize it further using Java.

Creating your Bambda

Two objects of the Montoya API are available to help you write your Bambda:

• LoggerCaptureHttpRequestResponse

• Utilities

To create a Bambda to filter which types of items Logger captures:

1. In the Logger tab, click the filter bar to open the Logger capture filter window.

2. In the Logger capture filter window, click Bambda mode.

3. Write your Bambda using Java.

4. Click Apply to compile and test the Bambda. Fix any errors shown in the Compilation errors panel. For more information, see Troubleshooting Bambdas.

5. [Optional] Click Save > Save. The Bambda is saved to your Bambda library for future use across Burp.

6. Click Apply & close.

Burp compiles your Bambda and applies it to any future traffic generated in this project.

Example Bambda

In the example below, we'll create a Bambda that filters Logger to capture only items that meet the following criteria:

• The item must not have a MIME type of WOFF or WOFF2.

In this example, our Bambda is:

var mimeType = requestResponse.mimeType(); return mimeType != MimeType.FONT_WOFF && mimeType != MimeType.FONT_WOFF2;