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.

CVSS v3 9.1 CRITICAL

9.1^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.2

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://cna.openjsf.org/security-advisories.html	Third Party Advisory
https://github.com/fastify/aws-lambda-fastify/security/advisories/GHSA-m93c-jj3f-68ph	Mitigation Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:fastify:fastify\/aws-lambda:6.4.0:*:*:*:*:node.js:*:*

History

No history.

Information

Published : 2026-08-03 16:16

Updated : 2026-09-04 13:44

NVD link : CVE-2026-18248

Mitre link : CVE-2026-18248

CVE.ORG link : CVE-2026-18248

JSON object : View

Products Affected

fastify

fastify\/aws-lambda

CWE

CWE-345

Insufficient Verification of Data Authenticity

{"id": "CVE-2026-18248", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-18248", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "total"}], "version": "2.0.3", "timestamp": "2026-08-03T19:35:01.188526Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "ce714d77-add3-4f53-aff5-83d477b104bb", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 9.1, "attackVector": "NETWORK", "baseSeverity": "CRITICAL", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}, "impactScore": 5.2, "exploitabilityScore": 3.9}]}, "affected": [{"source": "ce714d77-add3-4f53-aff5-83d477b104bb", "affectedData": [{"vendor": "@fastify/aws-lambda", "product": "@fastify/aws-lambda", "versions": [{"status": "affected", "version": "6.4.0", "lessThan": "6.4.1", "versionType": "semver"}, {"status": "unaffected", "version": "6.4.1", "versionType": "semver"}], "packageURL": "pkg:npm/@fastify/aws-lambda", "defaultStatus": "unaffected"}]}], "published": "2026-08-03T16:16:28.247", "references": [{"url": "https://cna.openjsf.org/security-advisories.html", "tags": ["Third Party Advisory"], "source": "ce714d77-add3-4f53-aff5-83d477b104bb"}, {"url": "https://github.com/fastify/aws-lambda-fastify/security/advisories/GHSA-m93c-jj3f-68ph", "tags": ["Mitigation", "Vendor Advisory"], "source": "ce714d77-add3-4f53-aff5-83d477b104bb"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "ce714d77-add3-4f53-aff5-83d477b104bb", "description": [{"lang": "en", "value": "CWE-345"}]}], "descriptions": [{"lang": "en", "value": "@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."}], "lastModified": "2026-09-04T13:44:16.757", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:fastify:fastify\\/aws-lambda:6.4.0:*:*:*:*:node.js:*:*", "vulnerable": true, "matchCriteriaId": "D6C7B2A3-A135-4087-B0F4-85C656A57576"}], "operator": "OR"}]}], "sourceIdentifier": "ce714d77-add3-4f53-aff5-83d477b104bb"}