Activity Task-Stack / Affinity Hijacking

← Improper Platform Usage

activity_task_stack_hijacking   HARD

Description

Loose task affinity / launch modes (singleTask + shared taskAffinity, allowTaskReparenting) let a malicious Activity insert itself into a trusted app’s task/back-stack (StrandHogg-style), so the attacker screen appears inside the victim’s flow for phishing / UI-trust confusion. Distinct from tapjacking (this is task-stack placement, not an overlay) (Android task-hijacking class).

How it works

Loose task affinity and launch modes (a malicious Activity declaring the victim app’s taskAffinity with singleTask or allowTaskReparenting) let the attacker insert itself into a trusted app’s task and back-stack. When the user returns to the victim app they are shown the attacker’s phishing screen inside the victim flow (StrandHogg). This is task-stack placement, distinct from a drawn tapjacking overlay, simulated offline and deterministically. The secure path enforces a unique per-app affinity and disallows reparenting, forcing the malicious activity into its own task so it can never appear in the victim flow.

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 Improper Platform Usage category (e.g. --dart-define-from-file=config/flavors/dev.json) and run on an Android emulator you control. The demo needs no external tooling; for the optional on-device reproduction the relevant tools are: adb, drozer, jadx.
2. Locate the target. From the home index, open Activity Task-Stack / Affinity Hijacking (activity_task_stack_hijacking). 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. From a co-resident/attacker context (adb shell am start/drozer, or a crafted deep link / QR), send the untrusted input to the exported component or WebView and confirm the app performs the unsafe action (navigation, JS execution, file/URI access) with no validation.
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)

• adb
• drozer
• jadx

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:

• malicious activity with matching taskAffinity

Real-world references

Concrete public disclosures that match this vulnerability class:

• OWASP MASTG: Android task hijacking (taskAffinity / launch-mode abuse)