
How UNC3569 Weaponized Trusted Software: The Sogou Input Method Supply Chain Attack
In April 2026, China-linked threat group UNC3569 exploited a critical vulnerability (CVE-2026-51990) in Sogou Input Method, a widely-used Chinese character input tool with over 455 million monthly users. The attackers leveraged a crafted sgbiz: link to bypass security controls and deploy the GRAYRABBIT backdoor through an outdated Chromium browser engine with disabled sandboxing. The exploit chain utilized a 2021 V8 JavaScript engine vulnerability (CVE-2021-38003) that had been patched in Chrome but remained unaddressed in Sogou's embedded browser, allowing remote code execution with user privileges. This incident highlights the growing sophistication of supply chain attacks targeting widely-deployed software components, particularly those serving large user bases in critical regions. The exploitation of years-old vulnerabilities in embedded browsers demonstrates how legacy code in trusted applications creates persistent attack surfaces for nation-state actors.
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