CVE-2026-18248
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk12th percentile - higher than 12% of all known CVEs
Summary
In @fastify/aws-lambda version 6.4.0, the decoration of Fastify requests with request.awsLambda.event and request.awsLambda.context is populated based on client-controlled HTTP headers (x-apigateway-event and x-apigateway-context) instead of the trusted internal token. An unauthenticated attacker can set a single HTTP header and forge the entire Lambda proxy event, including the authorizer context, leading to full authentication and authorization bypass and privilege escalation. Only version 6.4.0 is affected; the fix is in version 6.4.1.
Risk Assessment
The organization is exposed to a complete bypass of authentication and authorization mechanisms in applications using @fastify/aws-lambda, which can lead to unauthorized access to data and systems and privilege escalation.
Recommendation
Immediately upgrade @fastify/aws-lambda to version 6.4.1, which resolves the issue by using only the internal token and stripping reserved headers before processing the request.
Original NVD description (English source)
@fastify/aws-lambda version 6.4.0 decorates each Fastify request with request.awsLambda.event and request.awsLambda.context, values that applications are documented to use for authorization decisions such as reading API Gateway authorizer claims. In the default configuration, the getter that populates this decoration reads the client-controlled x-apigateway-event and x-apigateway-context HTTP headers before falling back to the trusted internal request token, and those reserved headers are not stripped from the incoming event. An unauthenticated attacker who can set a single HTTP header can therefore forge the entire Lambda proxy event, including the authorizer context, and override the genuine one. This results in a full authentication and authorization bypass and privilege escalation for any application that trusts request.awsLambda.event for identity or access control. Only version 6.4.0 is affected. Patches: upgrade to @fastify/aws-lambda 6.4.1, which resolves the decoration only through the internal per-invocation token and strips the reserved headers before the request is processed.