CVE-2026-18248 (CVSS 9.1)

Description

@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.

Is your site exposed to CVE-2026-18248?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

9.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS — Exploit Prediction

0.0022

Probability of exploitation

0.12%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-345 CWE-345

References

Other References

https://cna.openjsf.org/security-advisories.html https://github.com/fastify/aws-lambda-fastify/security/advisories/GHSA-m93c-jj3f-68ph

Frequently Asked Questions

What is CVE-2026-18248? +

@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. It has a CVSS v3.1 base score of 9.1 (CRITICAL).

How severe is CVE-2026-18248? +

CVE-2026-18248 has a CVSS v3.1 score of 9.1 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0022, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-18248? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-45022

go-git is an extensible git implementation library written in pure Go. Prior to 5.19.0 and 6.0.0-alpha.3, go-git may parse malformed …

CVE-2026-42206

Roadiz is a polymorphic content management system based on a node system. Prior to versions 2.3.43, 2.5.45, 2.6.31, and 2.7.18, …

CVE-2026-47202

Kavita is a cross platform reading server. Prior to 0.9.0.2, an Improper Token validation flaw permits a remote and unauthenticated …

CVE-2025-21606

stats is a macOS system monitor in for the menu bar. The Stats application is vulnerable to a local privilege …

CVE-2025-25188

Hickory DNS is a Rust based DNS client, server, and resolver. A vulnerability present starting in version 0.8.0 and prior …

CVE-2025-52484

RISC Zero is a general computing platform based on zk-STARKs and the RISC-V microarchitecture. Due to a missing constraint in …

CVE-2026-18248