TOCTOU Race Condition in Auth Check
toctou_race_condition HARD
| Category | Insufficient Resilience |
| OWASP Mobile (2024) | M7 |
| MASVS | MASVS-AUTH-1MASVS-CODE-4 |
| MASWE | MASWE-0018 |
| CWE | CWE-367 |
| Platform | AndroidiOS |
Description
Auth is checked then used with a mutable gap an attacker can win.
How it works
The withdrawal checks the balance, then debits it in a separate step. Between check and use, a second concurrent withdrawal sees the same stale balance and also succeeds, a double-spend. The exploit wins the race deterministically and persists the corrupted balance to on-disk storage.
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
- Set up. Build DVMA with a flavor that enables the Insufficient Resilience 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,r2frida,frida-trace. - Locate the target. From the home index, open TOCTOU Race Condition in Auth Check (
toctou_race_condition). The How it works section above describes this module’s specific weakness; the screen states the intended-secure behavior and exposes the vulnerable action. - Exploit. Attach an instrumentation tool (
frida/objection) and hook or patch the single client-side check, confirming the protection flips to ‘pass’ and the guarded functionality unlocks. - 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).
- 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.