Api Rate Abuse in Nestjs with Saml

Rate abuse in a NestJS application using SAML for authentication typically centers on the interaction between unauthenticated or pre-authentication endpoints and the SAML flow. Because SAML assertions are often processed in a dedicated route (e.g., /saml/acs), attackers can target that endpoint or related unauthenticated APIs to exhaust rate limits, bypass intended throttling, or amplify brute-force and enumeration risks.

Consider a typical NestJS setup where the SAML strategy validates assertions and establishes a session. Until the assertion is validated and a session or JWT is established, the user is effectively unauthenticated. If the SAML assertion consumer service (ACS) route or the metadata discovery endpoint lacks strict rate limits, an attacker can send many assertions or login requests in quick succession. This can lead to account lockouts for legitimate users (via invalid assertion floods) or resource exhaustion on the SAML service provider (SP) and identity provider (IdP) integrations.

Another vector involves endpoints that rely on incomplete authorization states. For example, if an endpoint checks for a session cookie but does not enforce rate limits for unauthenticated contexts, attackers can probe it directly even when SAML protects the primary application routes. In systems where SAML attributes are mapped to roles or permissions post-assertion, attackers may exploit missing rate controls on user registration or attribute assertion processing to create many synthetic identities or trigger expensive backend logic (e.g., provisioning, logging, or external calls).

OWASP API Top 10 highlights rate limiting as critical to prevent abuse. CVE patterns such as excessive requests leading to denial of service or bypass via alternative paths are relevant here. NestJS applications that integrate SAML must ensure that both the public endpoints involved in the SAML flow (e.g., /saml/acs, /saml/metadata) and any unauthenticated surfaces share coherent, rigorously enforced rate limits. Without this, the SAML integration can unintentionally widen the attack surface.

Implement SAML-specific rate limiting in NestJS by combining global guards or interceptors with route-level limits on SAML endpoints. Ensure that the limits are applied before assertion processing and metadata requests, and that they are coordinated with any existing global rate limiters to avoid gaps.

Example SAML setup with explicit rate-limited ACS route

import { Controller, Post, UseGuards, Req, Res } from '@nestjs/common';
import { AuthGuard } from '@nestjs/passport';
import { Request, Response } from 'express';
import { RateLimitGuard } from './rate-limit.guard'; // custom guard

@Controller('saml')
export class SamlController {
  constructor(private readonly samlAuthService: SamlAuthService) {}

  @Post('acs')
  @UseGuards(RateLimitGuard, AuthGuard('saml'))
  async acs(
    @Req() req: Request,
    @Res() res: Response,
  ) {
    // Process SAML assertion; RateLimitGuard ensures pre-check
    return this.samlAuthService.handleAssertion(req, res);
  }

  @Get('metadata')
  @UseGuards(RateLimitGuard)
  async metadata() {
    return this.samlAuthService.getMetadata();
  }
}

Define a rate-limit guard that uses a token bucket or fixed window suitable for your traffic profile. For example, using a NestJS interceptor that checks a distributed store (e.g., Redis) can help synchronize limits across instances:

import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';
import { RateLimiterRedis } from 'rate-limiter-flexible';
import { RedisClient } from 'redis';

@Injectable()
export class RateLimitGuard implements CanActivate {
  private limiter: RateLimiterRedis;

  constructor(redisClient: RedisClient) {
    this.limiter = new RateLimiterRedis({
      storeClient: redisClient,
      keyPrefix: 'saml_acs',
      points: 30,            // 30 requests
      duration: 60,          // per 60 seconds
      blockDuration: 60,     // block for 60 seconds if exceeded
    });
  }

  async canActivate(context: ExecutionContext): Promise {
    const request = context.switchToHttp().getRequest();
    const ip = request.ip;
    try {
      await this.limiter.consume(ip);
      return true;
    } catch (rejRes) {
      throw new HttpException('Too many requests', 429);
    }
  }
}

For broader protection, apply a global rate limiter to unauthenticated routes while ensuring SAML-specific routes are not inadvertently excluded. Combine with attribute-based rules to tighten limits for high-risk actions (e.g., initiating SAML requests or processing assertions with elevated scopes). Use standardized identifiers like the SAML NameID to correlate abusive patterns across assertions and prevent targeted enumeration.

Global rate limiting for public endpoints

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { RateLimiterRedis } from 'rate-limiter-flexible';
import { RedisClient } from 'redis';
import { HttpException, HttpStatus, INestApplication } from '@nestjs/common';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  const redisClient = new RedisClient({ url: process.env.REDIS_URL });

  const globalLimiter = new RateLimiterRedis({
    storeClient: redisClient,
    keyPrefix: 'global_unauth',
    points: 100,   // 100 requests
    duration: 60,  // per minute
  });

  app.use(async (req, res, next) => {
    // Skip SAML protected routes if you prefer separate controls
    const ip = req.ip;
    try {
      await globalLimiter.consume(ip);
      next();
    } catch {
      res.status(HttpStatus.TOO_MANY_REQUESTS).send('Too many requests');
    }
  });

  await app.listen(3000);
}
bootstrap();

Ensure that SAML endpoints are included in your API inventory and tested by middleBrick scans. The scanner checks rate limiting among 12 security controls and can highlight missing protections on SAML routes. If you need continuous monitoring, the Pro plan provides scheduled scans and alerts when rate limits are misconfigured or thresholds are frequently triggered.