# AWS - Lambda Enum

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## Lambda

Amazon Web Services (AWS) Lambda is described as a **compute service** that enables the execution of code without the necessity for server provision or management. It is characterized by its ability to **automatically handle resource allocation** needed for code execution, ensuring features like high availability, scalability, and security. A significant aspect of Lambda is its pricing model, where **charges are based solely on the compute time utilized**, eliminating the need for initial investments or long-term obligations.

To call a lambda it's possible to call it as **frequently as you wants** (with Cloudwatch), **expose** an **URL** endpoint and call it, call it via **API Gateway** or even based on **events** such as **changes** to data in a **S3** bucket or updates to a **DynamoDB** table.

The **code** of a lambda is stored in **`/var/task`**.

### Lambda Aliases Weights

A Lambda can have **several versions**.\
And it can have **more than 1** version exposed via **aliases**. The **weights** of **each** of the **versions** exposed inside and alias will decide **which alias receive the invocation** (it can be 90%-10% for example).\
If the code of **one** of the aliases is **vulnerable** you can send **requests until the vulnerable** versions receives the exploit.

![](<../../../images/image (223).png>)

### Resource Policies

Lambda resource policies allow to **give access to other services/accounts to invoke** the lambda for example.\
For example this is the policy to allow **anyone to access a lambda exposed via URL**:

<figure><img src="https://lh4.googleusercontent.com/4PNFKBdzr3nMrPqeKkTslgwWDKxkXMdQ1SNdv7NPHykj3GX8wODrQyXOFbjk4fxHfZ8pDm5ijWgk2Vq2EGXiPRT3TQfZf1fHycvdEKBuDxJDYos1CJeMHXSeg86ZB-Ol7CNtten6xkVFQj6AhDUEWNQJrQ=s2048" alt=""><figcaption></figcaption></figure>

Or this to allow an API Gateway to invoke it:

<figure><img src="https://lh3.googleusercontent.com/Su0JlR0wBqb-99Z4N_2-_kMlX0Xzx2n_GpZuOPW5IeXR3FYbm8OHFDM3Ora1BpXiSjHpDVUlq4yEyXwaI3nBuze6DJ-wRf2ATsCuWbq0wuBCd34E9uIpqwheE6Cc_PopviI_93O_j2ZKXc1-AJtsBoLVUw=s2048" alt=""><figcaption></figcaption></figure>

### Lambda Database Proxies

When there are **hundreds** of **concurrent lambda requests**, if each of them need to **connect and close a connection to a database**, it's just not going to work (lambdas are stateless, cannot maintain connections open).\
Then, if your **Lambda functions interact with RDS Proxy instead** of your database instance. It handles the connection pooling necessary for scaling many simultaneous connections created by concurrent Lambda functions. This allows your Lambda applications to **reuse existing connections**, rather than creating new connections for every function invocation.

### Lambda EFS Filesystems

To preserve and even share data **Lambdas can access EFS and mount them**, so Lambda will be able to read and write from it.

### Lambda Layers

A Lambda _layer_ is a .zip file archive that **can contain additional code** or other content. A layer can contain libraries, a [custom runtime](https://docs.aws.amazon.com/lambda/latest/dg/runtimes-custom.html), data, or configuration files.

It's possible to include up to **five layers per function**. When you include a layer in a function, the **contents are extracted to the `/opt`** directory in the execution environment.

By **default**, the **layers** that you create are **private** to your AWS account. You can choose to **share** a layer with other accounts or to **make** the layer **public**. If your functions consume a layer that a different account published, your functions can **continue to use the layer version after it has been deleted, or after your permission to access the layer is revoked**. However, you cannot create a new function or update functions using a deleted layer version.

Functions deployed as a container image do not use layers. Instead, you package your preferred runtime, libraries, and other dependencies into the container image when you build the image.

### 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**.

### Enumeration

```bash
aws lambda get-account-settings

# List functions and get extra config info
aws lambda list-functions
aws lambda get-function --function-name <function_name>
aws lambda get-function-configuration --function-name <function_name>
aws lambda list-function-event-invoke-configs --function-name <function_name>
## Check for creds in env vars
aws lambda list-functions | jq '.Functions[].Environment'
## Download & check the source code
aws lambda get-function --function-name "<func_name>" --query 'Code.Location'
wget -O lambda-function.zip <url-from-previous-query>

# Get Lambda URL (if any)
aws lambda list-function-url-configs --function-name <function_name>
aws lambda get-function-url-config --function-name <function_name>

# Get who has permissions to invoke the Lambda
aws lambda get-policy --function-name <function_name>

# Versions and Aliases
aws lambda list-versions-by-function --function-name <func_name>
aws lambda list-aliases --function-name <func_name>

# List layers
aws lambda list-layers
aws lambda list-layer-versions --layer-name <name>
aws lambda get-layer-version --layer-name <name> --version-number <ver>
aws lambda get-layer-version-by-arn --arn <name> #Get external ARNs

# List other metadata
aws lambda list-event-source-mappings
aws lambda list-code-signing-configs
aws lambda list-functions-by-code-signing-config --code-signing-config-arn <arn>
```

### Invoke a lambda

#### Manual

```bash
# Invoke function
aws lambda invoke --function-name FUNCTION_NAME /tmp/out
## Some functions will expect parameters, they will access them with something like:
## target_policys = event['policy_names']
## user_name = event['user_name']
aws lambda invoke --function-name <name> --cli-binary-format raw-in-base64-out --payload '{"policy_names": ["AdministratorAccess], "user_name": "sdf"}' out.txt
```

#### Via exposed URL

```bash
aws lambda list-function-url-configs --function-name <function_name> #Get lambda URL
aws lambda get-function-url-config   --function-name <function_name> #Get lambda URL
```

#### Call Lambda function via URL

Now it's time to find out possible lambda functions to execute:

```
aws --region us-west-2 --profile level6 lambda list-functions
```

![](<../../../images/image (262).png>)

A lambda function called "Level6" is available. Lets find out how to call it:

```bash
aws --region us-west-2 --profile level6 lambda get-policy --function-name Level6
```

![](<../../../images/image (102).png>)

Now, that you know the name and the ID you can get the Name:

```bash
aws --profile level6 --region us-west-2 apigateway get-stages --rest-api-id "s33ppypa75"
```

![](<../../../images/image (237).png>)

And finally call the function accessing (notice that the ID, Name and function-name appears in the URL): [https://s33ppypa75.execute-api.us-west-2.amazonaws.com/Prod/level6](https://s33ppypa75.execute-api.us-west-2.amazonaws.com/Prod/level6)

`URL:`**`https://<rest-api-id>.execute-api.<region>.amazonaws.com/<stageName>/<funcName>`**

#### Other Triggers

There are a lot of other sources that can trigger a lambda

<figure><img src="../../../images/image (167).png" alt=""><figcaption></figcaption></figure>

### Privesc

In the following page you can check how to **abuse Lambda permissions to escalate privileges**:

{{#ref}}
../aws-privilege-escalation/aws-lambda-privesc/README.md
{{#endref}}

### Unauthenticated Access

{{#ref}}
../aws-unauthenticated-enum-access/aws-lambda-unauthenticated-access/README.md
{{#endref}}

### Post Exploitation

{{#ref}}
../aws-post-exploitation/aws-lambda-post-exploitation/
{{#endref}}

### Persistence

{{#ref}}
../aws-persistence/aws-lambda-persistence/
{{#endref}}

## References

- [https://docs.aws.amazon.com/lambda/latest/dg/gettingstarted-concepts.html#gettingstarted-concepts-layer](https://docs.aws.amazon.com/lambda/latest/dg/gettingstarted-concepts.html#gettingstarted-concepts-layer)
- [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/)

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