hacktricks-cloud/pentesting-cloud/aws-security/aws-persistence/aws-lambda-persistence/aws-abusing-lambda-extensions.md

# AWS - Abusing Lambda Extensions

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## Lambda Extensions

Lambda extensions enhance functions by integrating with various **monitoring, observability, security, and governance tools**. These extensions, added via [.zip archives using Lambda layers](https://docs.aws.amazon.com/lambda/latest/dg/configuration-layers.html) or included in [container image deployments](https://aws.amazon.com/blogs/compute/working-with-lambda-layers-and-extensions-in-container-images/), operate in two modes: **internal** and **external**.

* **Internal extensions** merge with the runtime process, manipulating its startup using **language-specific environment variables** and **wrapper scripts**. This customization applies to a range of runtimes, including **Java Correto 8 and 11, Node.js 10 and 12, and .NET Core 3.1**.
* **External extensions** run as separate processes, maintaining operation alignment with the Lambda function's lifecycle. They're compatible with various runtimes like **Node.js 10 and 12, Python 3.7 and 3.8, Ruby 2.5 and 2.7, Java Corretto 8 and 11, .NET Core 3.1**, and **custom runtimes**.

For more information about [**how lambda extensions work check the docs**](https://docs.aws.amazon.com/lambda/latest/dg/runtimes-extensions-api.html).

### External Extension for Persistence, Stealing Requests & modifying Requests

This is a summary of the technique proposed in this post: [https://www.clearvector.com/blog/lambda-spy/](https://www.clearvector.com/blog/lambda-spy/)

It was found that the default Linux kernel in the Lambda runtime environment is compiled with “**process\_vm\_readv**” and “**process\_vm\_writev**” system calls. And all processes run with the same user ID, even the new process created for the external extension. **This means that an external extension has full read and write access to Rapid’s heap memory, by design.**

Moreover, while Lambda extensions have the capability to **subscribe to invocation events**, AWS does not reveal the raw data to these extensions. This ensures that **extensions cannot access sensitive information** transmitted via the HTTP request.

The Init (Rapid) process monitors all API requests at [http://127.0.0.1:9001](http://127.0.0.1:9001/) while Lambda extensions are initialized and run prior to the execution of any runtime code, but after Rapid.

<figure><img src="../../../../.gitbook/assets/image (254).png" alt=""><figcaption><p><a href="https://www.clearvector.com/blog/content/images/size/w1000/2022/11/2022110801.rapid.default.png">https://www.clearvector.com/blog/content/images/size/w1000/2022/11/2022110801.rapid.default.png</a></p></figcaption></figure>

The variable **`AWS_LAMBDA_RUNTIME_API`** indicates the **IP** address and **port** number of the Rapid API to **child runtime processes** and additional extensions.

{% hint style="warning" %}
By changing the **`AWS_LAMBDA_RUNTIME_API`** environment variable to a **`port`** we have access to, it's possible to intercept all actions within the Lambda runtime (**man-in-the-middle**). This is possible because the extension runs with the same privileges as Rapid Init, and the system's kernel allows for **modification of process memory**, enabling the alteration of the port number.
{% endhint %}

Because **extensions run before any runtime code**, modifying the environment variable will influence the runtime process (e.g., Python, Java, Node, Ruby) as it starts. Furthermore, **extensions loaded after** ours, which rely on this variable, will also route through our extension. This setup could enable malware to entirely bypass security measures or logging extensions directly within the runtime environment.

<figure><img src="../../../../.gitbook/assets/image (267).png" alt=""><figcaption><p><a href="https://www.clearvector.com/blog/content/images/size/w1000/2022/11/2022110801.rapid.mitm.png">https://www.clearvector.com/blog/content/images/size/w1000/2022/11/2022110801.rapid.mitm.png</a></p></figcaption></figure>

The tool [**lambda-spy**](https://github.com/clearvector/lambda-spy) was created to perform that **memory write** and **steal sensitive information** from lambda requests, other **extensions** **requests** and even **modify them**.

## References

* [https://aws.amazon.com/blogs/compute/building-extensions-for-aws-lambda-in-preview/](https://aws.amazon.com/blogs/compute/building-extensions-for-aws-lambda-in-preview/)
* [https://www.clearvector.com/blog/lambda-spy/](https://www.clearvector.com/blog/lambda-spy/)

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