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One-click remote code execution in Sogou Input Method
CVE-2026-51990 is a remote code execution vulnerability affecting Tencent Sogou Input Method for Windows before version 16.3.0.3498. The sgbiz custom protocol handler validates the requested component but passes attacker-controlled command-line arguments without adequate validation. These arguments can launch the skin-marketplace component and direct its embedded CEF webview to an arbitrary URL without scheme or destination restrictions. The webview uses outdated Chromium 80 with sandboxing and important web-security protections disabled. In observed attacks, a malicious page exploited the V8 vulnerability CVE-2021-38003 to execute arbitrary code with the signed-in user's permissions. UNC3569 exploited this one-click chain to deploy the GRAYRABBIT backdoor.
What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
A remote attacker can execute arbitrary code with the permissions of the signed-in Windows user after the victim opens a crafted protocol link. Observed exploitation installed GRAYRABBIT, enabling command execution, interactive shell access, system-information collection, bidirectional file transfer, and additional module loading. The vulnerability does not itself establish privilege escalation to SYSTEM.
If you can’t patch tonight, do this now.
Until the fixed release is deployed, restrict or disable use of the affected Sogou Input Method installation where operationally feasible and avoid opening untrusted sgbiz links. Monitor endpoint telemetry for anomalous Sogou component launches, unexpected child processes, and unusual outbound connections. Review historical endpoint, DNS, and proxy records for evidence of exploitation, block confirmed malicious infrastructure, and isolate suspected compromised devices.
Patch, then assume compromise.
Upgrade Sogou Input Method to version 16.3.0.3498 or later and verify that the automatic update has been installed. Released on April 21, 2026, the fix validates URL-bearing protocol-handler arguments, restricts them to HTTPS, and applies a hostname allowlist for approved Sogou and Tencent destinations. Continue applying subsequent updates: the protocol-handler fix did not update the obsolete embedded Chromium engine or restore its sandbox and disabled web-security protections.
No validated public exploits yet. Hidden: 1 rejected by Mallory's analysis as not a working exploit.
66 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.