Certain versions of WeChat, a popular messaging app created by tech giant Tencent, contain a type confusion vulnerability that could allow an adversary to execute remote code. While this issue, CVE-2023-3420, was disclosed and patched in the V8 engine in June 2023, the WeChat Webview component was not updated, and still remained vulnerable when Talos reported to Vendor in April 2024.  Cisco Talos researchers have confirmed that WeChat versions up to 8.0.42 (the latest version on the Google Play store for Android devices before June 14, 2024) were vulnerable to this issue. However, due to the dynamic WebView loading mechanism, Talos cannot confirm if it’s patched on all versions. Talos reported the vulnerability to Tencent WeChat on April 30, 2024, and continued our investigation in the following weeks and months. 

Vulnerability overview 

WeChat is an instant messenger application with a large user base in China. It also offers users the ability to pay for certain products through the app and includes several functionalities similar to other social media platforms like Facebook and X. 

During Cisco Talos’ research of WeChat, we uncovered that it employs a custom WebView component instead of relying on the built-in Android WebView. This component is a custom version of XWalk, maintained by Tencent, which consists of an embedded Chromium browser with V8 version 8.6.365.13 released on Oct. 12, 2020, supporting the rendering of HTML and the execution of JavaScript. 

The custom WebView component is dynamically downloaded onto the phone after the user logs into the app for the first time, allowing Tencent to deploy dynamic updates. When downloaded, XWalk webview is located at the path `/data/data/com.tencent.mm/app_xwalk_4433/apk/base.apk`. The library at /data/data/com.tencent.mm/app_xwalk_4433/extracted_xwalkcore/libxwebcore.so contains an embedded browser environment with an outdated version of V ..

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