Windows
CVE-2026-25961
HIGH
Severity by source
AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Lifecycle Timeline
3DescriptionGitHub Advisory
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.
AnalysisAI
SumatraPDF versions 3.5.0 through 3.5.2 fail to validate TLS certificates during software updates and execute installers without signature verification, allowing network attackers to perform man-in-the-middle attacks and inject malicious code. An attacker with any valid TLS certificate can intercept update requests and redirect users to a malicious installer, achieving arbitrary code execution on Windows systems. Public exploit code exists for this vulnerability and no patch is currently available.
Technical ContextAI
Classified as CWE-295 (Improper Certificate Validation). Affects Sumatrapdf. 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.
RemediationAI
Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.
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External POC / Exploit Code
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