SumatraPDF is a multi-format reader for Windows. In 3.5.0 through 3.5.2, SumatraPDFs update mechanism disables TLS hostname verification (INTERNET_FLAG_IGNORE_CERT_CN_INVALID) and executes installers without signature checks. A network attacker with any valid TLS certificate (e.g., Lets Encrypt) can intercept the update check request, inject a malicious installer URL, and achieve arbitrary code execution.
Weakness
The product does not validate, or incorrectly validates, a certificate.