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CVE-2026-18248

Status: AnalyzedCritical (9.1)—

@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.

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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

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

🎯 ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

AV:N/PR:N permite acceso remoto sin privilegios (T1190). El atacante forja headers HTTP para falsificar identidad y autorización (T1078), escalando a admin mediante bypass de controles de acceso (T1068).

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

🛡️ ATT&CK mitigations that cover these techniques

Privileged Account ManagementApplication Isolation and SandboxingExploit ProtectionUpdate SoftwareApplication Developer GuidanceActive Directory Configuration

Affected technologies (1)

Fastify — Fastify/aws-lambda

CWEs

References

Raw JSON (NVD)

Show
{
  "id": "CVE-2026-18248",
  "cveTags": [],
  "metrics": {
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          "options": [
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          "integrityImpact": "HIGH",
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  "published": "2026-08-03T16:16:28.247",
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  "lastModified": "2026-09-04T13:44:16.757",
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