AWS Application Load Balancer processes HTTP/2 requests inconsistently when the WAF is enabled, allowing a remote actor to fragment a request body across frames so that only a partial body is inspected by AWS WAF. The vulnerability is a cross‑decoding issue (CWE‑444) and enables malicious payloads to evade WAF rules that normally inspect the entire request body. The resulting impact is the loss of protection that the WAF provides for the target application.

The affected systems are Amazon Web Services Application Load Balancers that have AWS WAF enabled on target groups using HTTP/2. Only HTTP/2 target groups are impacted; the vulnerability does not exist for HTTP/1.x traffic or for App Load Balancer configurations without WAF.

With a CVSS score of 7.9 the severity is considered high. The EPSS score is not available, and the vulnerability is not listed in the CISA KEV catalog. The likely attack vector is a remote attacker sending a crafted HTTP/2 request that splits a malicious payload across multiple frames, so the WAF sees only a benign fragment. The exploit conditions require the attacker to have network access to the ALB endpoint and the ALB must be configured to evaluate WAF rules only after reading sufficient body data. Because the exploit is possible but no public exploitation has been reported, the risk is moderate to high depending on the exposure of the target application.