Insecure / Bypassable Biometric Prompt

← Insecure Authentication / Authorization

insecure_biometric_prompt   MEDIUM

Description

Local auth is event-bound UI only; failure path is trivially bypassed.

How it works

The biometric prompt is decorative: success or failure just flips a client-side boolean and the protected secret is already in memory. Nothing is cryptographically bound to a Keystore/Keychain key that requires user authentication, so a frida hook or a patched boolean unlocks it. The buttons simulate the auth callbacks. A secure design binds the secret to a key that only releases after real user authentication.

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: frida, objection, r2frida, frida-trace.
2. Locate the target. From the home index, open Insecure / Bypassable Biometric Prompt (insecure_biometric_prompt). 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.
6. Map it back. Cross-reference the MASTG v2 test(s) MASTG-TEST-0327, MASTG-TEST-0266, MASTG-TEST-0267, MASTG-TEST-0329 for the canonical procedure and remediation.

Tools (optional)

• frida
• objection
• r2frida
• frida-trace

Real-world references

Concrete public disclosures that match this vulnerability class:

• CVE-2025-48528 (Android biometric UI overlay)