How to Fix AWS EC2 403 Forbidden and Permission Denied Errors

Understanding AWS EC2 403 Forbidden Errors

An AWS EC2 403 Forbidden error indicates that the server understands the request but refuses to authorize it. Unlike a 401 Unauthorized error (which implies missing or invalid authentication), a 403 means the identity is known, but the permissions are insufficient. In an AWS ecosystem, this error can originate from several layers: the EC2 instance's IAM role, an Application Load Balancer (ALB), AWS WAF, or the web server software (Nginx, Apache) running on the instance.

When troubleshooting, you might also encounter related errors like 502 Bad Gateway (often an ALB failing to communicate with the EC2 target), Connection Refused (Security Group or service down), or Timeout / Throttling (AWS API rate limits).

Step 1: Diagnose the Origin of the 403

Before applying fixes, you must determine which component is returning the 403.

1. Check the Web Server Logs: Connect to your EC2 instance and inspect the access/error logs for Nginx (/var/log/nginx/error.log) or Apache (/var/log/apache2/error.log). If the 403 originates here, it's likely a file permission issue or web server misconfiguration.
2. Inspect AWS WAF Logs: If your EC2 instance sits behind an ALB or CloudFront distribution integrated with AWS WAF, WAF might be blocking the request. Check the WAF sampled requests or Athena queries for AWS WAF logs. Look for the terminatingRuleId.
3. Review CloudTrail for IAM Issues: If your application on the EC2 instance is getting a 403 (or AccessDenied) when trying to access other AWS services (like S3 or DynamoDB), the instance's IAM role is the culprit. Search AWS CloudTrail for AccessDenied events associated with the instance's role session.

Step 2: Fix IAM Instance Profile Permissions

If your EC2 instance cannot access an S3 bucket or invoke an API, you need to update its IAM role.

1. Navigate to the EC2 Console > Instances.
2. Select your instance and check the Security tab for the attached IAM role.
3. Click the role to open the IAM console.
4. Review the attached policies. Ensure the role has explicit Allow permissions for the required actions and resources.
5. Example: If the app needs S3 read access, ensure s3:GetObject is allowed for the specific bucket ARN.

Step 3: Resolve AWS WAF Blocking

If AWS WAF is returning the 403:

1. Identify the triggered rule in the WAF console.
2. If it's a false positive from an AWS Managed Rule (e.g., SQLi or XSS rules blocking legitimate payloads), you can set the specific rule to Count mode or add an exception.
3. If you are hitting rate limits (aws ec2 rate limit or throttling), adjust the threshold of your rate-based rule if the traffic is legitimate.

Step 4: Fix Web Server File Permissions

If Nginx or Apache is throwing the 403:

1. Ensure the web server user (usually www-data or nginx) has read access to the web directory.
2. Run sudo chown -R www-data:www-data /var/www/html (adjust path as needed).
3. Run sudo find /var/www/html -type d -exec chmod 755 {} \;
4. Run sudo find /var/www/html -type f -exec chmod 644 {} \;

Handling Related Errors: 502, Connection Refused, and Timeouts

• 502 Bad Gateway: The ALB cannot reach the EC2 instance. Verify the web service (e.g., Node.js, Nginx) is actually running on the instance and listening on the port configured in the Target Group.
• Connection Refused: Check your EC2 Security Groups and Network ACLs. Ensure the inbound rules allow traffic on the required ports (80, 443, 22) from the expected source IPs.
• Timeout: Often caused by Security Groups dropping packets (no route) rather than actively refusing them. Also, verify the instance has a public IP or is correctly routed through a NAT Gateway if in a private subnet.