Executive brief
AWS Application Load Balancer (ALB) has a vulnerability where it may fail to properly inspect the full content of certain web requests when AWS WAF is enabled. An attacker could bypass security rules by splitting a malicious request into multiple parts, potentially allowing unauthorized or harmful traffic to reach your backend servers. This issue specifically affects load balancers configured to use HTTP/2 for their target groups.
Technical details
A vulnerability classified as CWE-444 (Inconsistent Interpretation of HTTP Requests) exists in AWS Application Load Balancer when integrated with AWS WAF. The flaw stems from how the ALB handles HTTP/2 multi-frame request bodies; an attacker can fragment a request body across multiple frames such that the WAF only inspects a partial body, effectively bypassing security rules. This issue specifically impacts ALB target groups configured for HTTP/2. AWS has released a remediation via a new target group attribute, 'Inspect after sufficient data', which forces the ALB to accumulate data frames before performing WAF inspection.
Affected products
- AWS Application Load Balancer (ALB) All versions using HTTP/2 target groups
Timeline
- 2026-05-22: patched: Remediation configuration option released by AWS
- 2026-06-29: disclosed: Public advisory and CVE published