Username Enumeration

← Insecure Authentication / Authorization

username_enumeration   EASY

Description

Login returns distinguishable responses for valid vs invalid usernames, allowing account enumeration.

How it works

The login helper returns “No such user” for an unknown account but “Invalid password” for a real account with the wrong password. By observing which error comes back, an attacker enumerates valid usernames without knowing any password. A secure login returns a single generic error for every failure.

How to exercise it. DVMA is the harness - open this module from the home index and tap the demo action. The screen ships the malicious input and simulates the attacker (e.g. the companion app, crafted intent, or scanned payload) in-process, and the evidence panel prints the proof. The Tools (optional) and Attack inputs below are only needed to reproduce the exploit end-to-end on a real device.

Exploit steps

1. Set up. Build DVMA with a flavor that enables the Insecure Authentication / Authorization category (e.g. --dart-define-from-file=config/flavors/dev.json) and run on an emulator/simulator you control. The demo needs no external tooling; for the optional on-device reproduction the relevant tools are: Burp Suite, mitmproxy.
2. Locate the target. From the home index, open Username Enumeration (username_enumeration). The How it works section above describes this module’s specific weakness; the screen states the intended-secure behavior and exposes the vulnerable action.
3. Exploit. Drive the authentication/authorization path, capture the token / assertion / decision, then replay or tamper with it (mitmproxy, a WebAuthn test harness, or by editing the value) and confirm the server-side check accepts the manipulated request.
4. Observe the evidence. Trigger the vulnerable action and read the evidence panel - it prints the concrete proof (leaked value, accepted replay, executed payload, or unauthorized result).
5. Contrast with the secure path. Run the module’s secure/hardened action (where provided) and confirm the same attack is rejected - this is what a correct implementation should do.

Tools (optional)

• Burp Suite
• mitmproxy