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Fix Broken User Authentication in NestJS

Broken User Authentication (OWASP A07:2021) is the death knell of an API. In NestJS, developers often fail by using weak hashing, hardcoded secrets, or neglecting brute-force protection. This guide strips out the garbage to implement a hardened Passport-JWT flow with Bcrypt and Rate Limiting.

The Vulnerable Pattern

@Injectable()
export class AuthService {
  async login(user: any) {
    // VULNERABILITY: Plaintext password comparison and hardcoded secret
    const foundUser = await this.usersService.findOne(user.email);
    if (foundUser && foundUser.password === user.password) {
      const payload = { sub: foundUser.id };
      return {
        access_token: jwt.sign(payload, 'SECRET_KEY'), // Hardcoded secret
      };
    }
    return null;
  }
}

The Secure Implementation

The vulnerable code is a gift to attackers: 1. Plaintext/MD5 storage allows instant credential harvesting if the DB is leaked. 2. Hardcoded secrets enable trivial JWT forgery. 3. Lack of rate limiting facilitates high-velocity brute-force and credential stuffing. The secure version mitigates this by: 1. Using Bcrypt (work factor 12+) for computationally expensive hashing. 2. Enforcing short-lived JWTs (15m) signed with environment-injected secrets. 3. Implementing the NestJS ThrottlerModule to drop connections from automated brute-force tools.

@Injectable()
export class AuthService {
  constructor(
    private usersService: UsersService,
    private jwtService: JwtService,
    private configService: ConfigService
  ) {}

async validateUser(email: string, pass: string): Promise {
const user = await this.usersService.findOne(email);
// SECURE: Use bcrypt with salt to prevent rainbow table attacks
const isMatch = await bcrypt.compare(pass, user.password);
if (user && isMatch) {
const { password, …result } = user;
return result;
}
return null;
}


async login(user: any) {
const payload = { sub: user.userId, email: user.email };
return {
access_token: this.jwtService.sign(payload, {
secret: this.configService.get(‘JWT_SECRET’),
expiresIn: ‘15m’, // Short-lived tokens
}),
};
}
}


// In app.module.ts: Implement Rate Limiting
@Module({
imports: [
ThrottlerModule.forRoot([{ ttl: 60000, limit: 5 }]),
],
})

System Alert • ID: 6668
Target: NestJS API
Potential Vulnerability

Your NestJS API might be exposed to Broken User Authentication

74% of NestJS apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.

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