Deep Link Regex DoS (ReDoS)

← Input Validation (OWASP Mobile M4)

deeplink_regex_dos   MEDIUM

Description

A catastrophically-backtracking regex parses incoming deep-link URLs, so a crafted link freezes/hangs the app (Mattermost CVE-2024-3872 class).

How it works

A catastrophically-backtracking regex (a nested-quantifier pattern like ^(a+)+$) parses incoming deep-link URLs. A crafted link, a long run of a repeated character followed by one non-matching char, forces the engine into exponential backtracking (about 2^(n-1) steps), freezing the app on the main isolate (the Mattermost CVE-2024-3872 class). This demo actually executes ^(a+)+$ against the crafted input and measures real wall-clock time with a Stopwatch; the ambiguous run is clamped to about 26 chars so the blow-up is observable (hundreds of ms to a few seconds) but bounded so it returns. The secure parser uses a linear, anchored, non-backtracking pattern whose cost grows linearly with input length.

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 Input Validation (OWASP Mobile M4) 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: Android: adb, jadx · iOS: xcrun simctl openurl, class-dump.
2. Locate the target. From the home index, open Deep Link Regex DoS (ReDoS) (deeplink_regex_dos). 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. Feed the crafted/malformed input (serialized blob, intent extra, media file, deep link) into the parsing path and confirm the app trusts it - state change, crash/DoS, or code path it should reject.
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)

Android

• adb
• jadx

iOS

• xcrun simctl openurl
• class-dump

Attack inputs

Payloads/artifacts you author for the on-device attack. The demo already ships and simulates these in-process (e.g. the malicious companion app / crafted intent is emulated inside the screen), so you only need to craft them to reproduce the exploit on a real device:

• crafted deep link