A critical vulnerability in Amazon CloudFront allows attackers to bypass WAF security inspections, potentially exposing backend services to malicious payloads.

This vulnerability involves the inconsistent interpretation of HTTP/2 requests, where an unauthenticated attacker can fragment a request body across multiple frames. This fragmentation causes the AWS WAF to inspect only a partial body, effectively bypassing configured security rules.

The ability to bypass WAF inspections poses a significant risk to the integrity and security of web applications protected by CloudFront. With a CVSS score of 9.8, this flaw could allow attackers to deliver exploits that would otherwise be blocked, leading to data breaches or unauthorized command execution. The resulting impact includes potential system compromise and the loss of sensitive customer data.

Immediate Action: No customer action is required as AWS has remediated this issue server-side.

Proactive Monitoring: Review historical access logs for suspicious HTTP/2 request patterns that may have targeted your environment prior to the server-side fix.

Compensating Controls: Ensure that additional defense-in-depth measures, such as input validation at the application layer, are maintained to reduce reliance solely on perimeter WAF rules.

Public Exploit Available: Unknown

While AWS has addressed this vulnerability on the server side, organizations should verify their security configurations and ensure their logging mechanisms are robust. It is recommended to perform a thorough audit of your WAF rules to ensure they are functioning as expected following this infrastructure update.