CVE-2026-54288 Overview
CVE-2026-54288 is an insufficient verification of data authenticity vulnerability [CWE-345] in the Hono web application framework. The flaw resides in the Body Limit Middleware, which trusts the client-supplied Content-Length header to enforce request body size limits. On AWS Lambda deployments (API Gateway v1/v2, ALB, VPC Lattice, and Lambda@Edge), the request body is delivered fully buffered and the adapter constructs requests using the declared Content-Length. An attacker can declare a small Content-Length while sending a much larger payload, bypassing the configured size limit. The vulnerability affects Hono versions prior to 4.12.25 and is fixed in 4.12.25.
Critical Impact
Attackers can bypass Hono Body Limit Middleware on AWS Lambda adapters by spoofing the Content-Length header, enabling oversized payload processing and resource consumption beyond enforced limits.
Affected Products
- Hono web application framework versions prior to 4.12.25
- Hono applications deployed on AWS Lambda with API Gateway v1 or v2
- Hono applications deployed on AWS Application Load Balancer (ALB), VPC Lattice, or Lambda@Edge
Discovery Timeline
- 2026-06-22 - CVE-2026-54288 published to NVD
- 2026-06-23 - Last updated in NVD database
Technical Details for CVE-2026-54288
Vulnerability Analysis
The Hono Body Limit Middleware enforces request body size restrictions by inspecting the incoming Content-Length header. On standard Node.js or runtime adapters, this value reflects the actual streamed body. However, the AWS Lambda adapters receive a fully buffered payload from the upstream AWS service and reconstruct the Request object using the client-declared Content-Length. The middleware never validates the header against the true buffered payload length.
This mismatch creates an authenticity verification gap. The middleware accepts attacker-controlled metadata as ground truth for an authorization decision about body size.
Root Cause
The root cause is improper trust of client-supplied data [CWE-345]. The middleware compares Content-Length to its configured limit instead of measuring the actual buffered body. On AWS Lambda runtimes, the upstream service does not normalize or correct the header before delivering the payload to the Hono adapter.
Attack Vector
An attacker sends an HTTP request to a Hono application running behind API Gateway, ALB, VPC Lattice, or Lambda@Edge. The request declares a Content-Length value below the configured Body Limit threshold while the actual body contains a much larger payload. The middleware reads the header, determines the request is within limits, and forwards the full buffered body to downstream handlers. Downstream code processes a payload larger than the application intended to allow, leading to excess memory consumption, increased Lambda execution costs, or denial of service against parsing logic.
No verified public proof-of-concept is available. See the GitHub Security Advisory GHSA-rv63-4mwf-qqc2 for upstream technical details.
Detection Methods for CVE-2026-54288
Indicators of Compromise
- Requests where the actual received body byte count exceeds the declared Content-Length header value
- Lambda invocations processing payload sizes larger than the configured Body Limit Middleware threshold
- Anomalous spikes in Lambda memory usage or execution duration on routes protected by Body Limit Middleware
Detection Strategies
- Log both the declared Content-Length header and the actual buffered body length at the adapter boundary, and alert when they diverge
- Inspect AWS CloudWatch Logs for Lambda functions running Hono for body-size anomalies and parsing errors on size-restricted endpoints
- Deploy WAF rules at API Gateway, CloudFront, or ALB to enforce maximum request body size independently of application-layer checks
Monitoring Recommendations
- Monitor Lambda MemoryUtilization and Duration CloudWatch metrics for outliers on endpoints expected to receive small payloads
- Track HTTP request patterns where small Content-Length values correlate with elevated downstream processing time
- Audit dependency manifests (package.json, package-lock.json) across CI/CD pipelines for Hono versions below 4.12.25
How to Mitigate CVE-2026-54288
Immediate Actions Required
- Upgrade Hono to version 4.12.25 or later across all AWS Lambda deployments
- Inventory all Lambda functions, Lambda@Edge functions, and ALB targets using Hono adapters and confirm the installed version
- Configure AWS WAF or API Gateway request size limits as a defense-in-depth control independent of application middleware
Patch Information
The maintainers fixed CVE-2026-54288 in Hono 4.12.25. The patch validates actual buffered body length on AWS Lambda adapters rather than trusting the client-declared Content-Length. Review the Hono Security Advisory GHSA-rv63-4mwf-qqc2 for full release notes and upgrade guidance.
Workarounds
- Enforce a maximum payload size at API Gateway, CloudFront, or ALB before requests reach the Hono adapter
- Implement a custom middleware that measures the actual Buffer.byteLength of the request body and rejects oversized payloads
- Restrict route exposure for size-sensitive endpoints until the upgrade to 4.12.25 is deployed
# Upgrade Hono to the patched release
npm install hono@^4.12.25
# Verify the resolved version
npm ls hono
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
