Revisiting BAT Browsers: Protecting At-Risk Populations from Surveillance, Censorship, and Targeted Attacks

All six Chinese browsers (Baidu Searchbox, UC Browser, QQ Browser, OPPO, Redmi/Mi, VIVO) transmit the full URL of every page visited—including HTTPS pages—along with page titles and search terms out-of-band to vendor servers, entirely bypassing VPN tunnel protection. In five of six cases this data is transmitted with no cryptography or weak cryptography (purely symmetric AES with hardcoded keys, or textbook RSA with a 128-bit modulus factorable in under 3 seconds), making it readable by any on-path actor between the VPN egress and the vendor's servers.

§4.1 detection dpikeyword-filtering cn

Chinese browsers transmit GPS coordinates alongside persistent user IDs (IMEI, GAID, CUID) and client IPs to vendor servers with poor transport security; an attacker with access to this stream can trivially detect VPN use without any DPI—GPS coordinates placing a user inside China combined with a non-Chinese client IP is an unambiguous VPN-use signal. This correlation attack succeeds against VPNs with perfect traffic obfuscation because the detection side-channel is entirely outside the encrypted tunnel.

§5, §6 detection ip-blockingtraffic-shape cn

Of the four Chinese browsers offering incognito mode (Baidu Searchbox, UC Browser, QQ Browser, Redmi/Mi), all four continue to leak PII and three continue to transmit full browsing activity including URLs; UC Browser specifically sends data during incognito sessions encrypted with hardcoded AES/CBC key "Ine34@32b#jeRs2h" and a zero initialization vector to crash-upload endpoints. Incognito mode in these browsers provides no protection against vendor-side or on-path surveillance and creates false privacy expectations for circumvention tool users.

§4.2 evaluation dpi cn

PWA-based circumvention tools that display their name or any identifying string in the browser URL bar or page title expose that identifier to all six Chinese browser vendors' telemetry servers, since all six browsers collect page titles and full URLs. Browser SDKs with READ_PHONE_STATE and elevated permissions can monitor PWA activity at the OS level in ways not possible with standard browsers, making browser selection as security-critical as the circumvention tool itself for the Tor Browser threat model.

§5, §6 defense keyword-filtering cn

All six browsers grant dangerous Android permissions (READ_PHONE_STATE, INTERNET, ACCESS_NETWORK_STATE) to third-party SDKs; built-in phone browsers grant significantly more such permissions than app-store browsers. Baidu Mobile Tongji Analytics SDK—present in all six via Baidu as default search engine—collects IMEI, UUID, CUID, GAID, device MAC, and Bluetooth MAC, creating a persistent cross-app device fingerprint that identifies users across VPN sessions and survives IP changes.

§4.3 detection dpikeyword-filtering cn