Resolving AWS CloudFront 403 Forbidden Errors: A Complete Troubleshooting Guide

Understanding the AWS CloudFront 403 Forbidden Error

When a user requests content through Amazon CloudFront and receives a 403 Forbidden HTTP status code, it signifies that the server understood the request but refuses to authorize it. In the context of CloudFront, this error rarely originates from the CDN edge nodes themselves unless specific edge configurations (like WAF or Geo-Restrictions) are triggered. Most commonly, the 403 error is bubbled up from the underlying origin server—such as an Amazon S3 bucket, an Application Load Balancer (ALB), or an API Gateway.

Troubleshooting this error requires isolating the layer rejecting the request. Is it AWS WAF blocking a malicious IP? Is S3 denying read access due to a missing Origin Access Control (OAC) policy? Or is it a custom backend application returning a 403?

Step 1: Diagnose the Request Path

The first step is identifying where the 403 is generated. CloudFront adds specific HTTP response headers that provide clues.

Run a curl command with verbose output:

curl -I -v https://d111111abcdef8.cloudfront.net/index.html

Examine the response headers. If you see Server: AmazonS3, the 403 is coming directly from your S3 origin. If you see X-Cache: Error from cloudfront, CloudFront itself (or an attached WAF) might be blocking the request.

Analyzing CloudFront Logs

Enable standard logging or real-time logs in your CloudFront distribution to capture the x-edge-detailed-result-type. If WAF is attached, check the WAF sampled requests to see if a specific WebACL rule is terminating the connection.

Step 2: Fixing S3 Origin 403 Errors

Amazon S3 is the most common origin for CloudFront. S3 returns a 403 Access Denied for two primary reasons: lacking permissions or requesting a missing object without s3:ListBucket permissions.

Scenario A: Missing Origin Access Control (OAC)

If your S3 bucket is strictly private (as it should be), CloudFront needs permission to fetch objects. Legacy setups used Origin Access Identity (OAI), but AWS now recommends Origin Access Control (OAC).

1. Go to the CloudFront Console -> Security -> Origin access.
2. Create an OAC for S3.
3. Go to your Distribution -> Origins -> Edit your S3 origin.
4. Select 'Origin access control settings' and choose the OAC you created.
5. Crucially, you must update the S3 Bucket Policy to allow this OAC. CloudFront provides a policy statement you can copy.

Scenario B: Missing Default Root Object

If you request https://example.com/ and get a 403, but https://example.com/index.html works perfectly, your distribution lacks a Default Root Object.

1. Open your CloudFront Distribution settings.
2. Edit the General settings.
3. In the 'Default root object' field, enter index.html.
4. Save changes and wait for the distribution to deploy.

Scenario C: Object Does Not Exist (Masked as 403)

By default, if an S3 bucket is private and an unauthenticated user requests an object that does not exist, S3 returns 403 Forbidden instead of 404 Not Found to prevent object discovery. To fix this in a Single Page Application (SPA) like React or Angular, configure CloudFront Custom Error Responses to intercept 403s and return index.html with a 200 OK status code.

Step 3: Resolving AWS WAF and Rate Limit 403s

If you are using AWS WAF attached to your CloudFront distribution, you may encounter 403 Forbidden errors due to rate limiting or managed rule groups.

When users experience an aws cloudfront rate limit error, it means a rate-based rule in your WebACL has been triggered. The default behavior for a blocked request is to return a 403 status.

1. Open the AWS WAF Console and select your WebACL (Region: Global/CloudFront).
2. Navigate to the 'Traffic overview' or 'Sampled requests' tab.
3. Filter for blocked requests. Identify the rule that triggered the block.
4. If a rate-based rule is too aggressive (e.g., blocking legitimate API traffic), increase the rate limit threshold (minimum is 100 requests per 5 minutes per IP).
5. Alternatively, add scope-down statements to exclude static assets (images, CSS) from rate limiting so only dynamic API calls are counted.

Step 4: Tackling Custom Origin Timeouts

Sometimes, an aws cloudfront timeout manifests as a 504 Gateway Timeout, but certain custom origins might abruptly close connections resulting in a 403 or 502.

If your custom origin takes longer to respond than the configured CloudFront Origin Read Timeout (default 30 seconds), CloudFront drops the connection.

1. Check your origin server logs (ALB, Nginx, Apache) to ensure the request is actually arriving and being processed.
2. If your application legitimately requires more time (e.g., a heavy report generation endpoint), increase the Origin Read Timeout in the CloudFront Origin settings (up to 60 seconds).
3. Ensure your origin's Keep-Alive timeout is strictly greater than CloudFront's timeout settings to prevent the origin from closing the connection prematurely.

Conclusion

Fixing a CloudFront 403 Forbidden error is an exercise in tracing the request lifecycle. By methodically checking S3 bucket policies, configuring proper default root objects, auditing AWS WAF rules for rate limits, and ensuring proper timeout thresholds, you can restore service and ensure a seamless content delivery experience.