Time-of-check Time-of-use (TOCTOU) Race Condition Affecting @nestjs/platform-fastify package, versions <11.1.11
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published30 Dec 2025
- disclosed29 Dec 2025
- creditHacktron AI
Introduced: 29 Dec 2025
CVE-2025-69211 (opens in a new tab)How to fix?
Upgrade @nestjs/platform-fastify to version 11.1.11 or higher.
Overview
@nestjs/platform-fastify is a Nest - modern, fast, powerful node.js web framework (@platform-fastify)
Affected versions of this package are vulnerable to Time-of-check Time-of-use (TOCTOU) Race Condition in the URL encoding middleware, allowing it to be bypassed in certain configurations. An attacker can gain unauthorized access to protected routes or administrative endpoints.
To be vulnerable, an application must be applying security checks via NestMiddleware/MiddlewareConsumer or app.use(), and must apply middleware to specific routes using string paths or controllers. See the vulnerable example below.
// app.module.ts
export class AppModule implements NestModule {
configure(consumer: MiddlewareConsumer) {
consumer
.apply(AuthMiddleware) // security check
.forRoutes('admin'); // string-based rule
}
}
PoC
Target Route: /admin
Middleware Path: admin
Attack Request: GET /%61dmin
Result: Middleware is skipped (no match on %61dmin), but controller for /admin is executed.