CVE-2026-25961: Sumatrapdfreader Sumatrapdf

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

SumatraPDF is a multi-format reader for Windows. In 3.5.0 through 3.5.2, SumatraPDF's 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., Let's Encrypt) can intercept the update check request, inject a malicious installer URL, and achieve arbitrary code execution.

Affected products

• Sumatrapdfreader Sumatrapdf: from 3.5, up to and including 3.5.2

Published 2026-02-09. Last modified 2026-06-17.