Tencent GameLoop before 4.1.21.90 downloaded updates over an insecure HTTP connection. A malicious attacker in an MITM position could spoof the contents of an XML document describing an update package, replacing a download URL with one pointing to an arbitrary Windows executable. Because the only integrity check would be a comparison of the downloaded file's MD5 checksum to the one contained within the XML document, the downloaded executable would then be executed on the victim's machine.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-33879
• https://github.com/mmiszczyk/cve-2021-33879
• https://www.gameloop.com