Biometric Result Not Bound to Operation

← Insecure Authentication / Authorization

biometric_authorization_not_bound   HARD

Description

The biometric prompt returns a boolean success that is NOT cryptographically bound to the specific operation being authorized (no CryptoObject / no signed server challenge), and the prompt UI can be overlaid, so a success is replayed or spoofed onto a different sensitive operation - authorization is decoupled from the biometric event (Android BiometricPrompt overlay CVE-2025-48528 class). Distinct from a trivially-bypassed prompt.

How it works

The biometric prompt returns a bare boolean success that is not cryptographically bound to the operation being authorized (no CryptoObject, no signed server challenge). A success the user gave for a low-value operation (view balance) is therefore replayed to authorize a different sensitive operation (a wire transfer), and an overlaid prompt lets an attacker capture or redirect the result (Android BiometricPrompt CVE-2025-48528 class). The secure path binds the biometric result to a per-operation signed challenge, so the token only authorizes the exact operation it was minted for.

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 Biometric Result Not Bound to Operation (biometric_authorization_not_bound). 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 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)