sumatrapdfreader SumatraPDF up to 3.5.2 on Windows Installer certificate validation

Summaryinfo

A vulnerability marked as critical has been reported in sumatrapdfreader SumatraPDF up to 3.5.2 on Windows. The impacted element is an unknown function of the component Installer Handler. This manipulation causes certificate validation. This vulnerability is registered as CVE-2026-25961. Remote exploitation of the attack is possible. Furthermore, an exploit is available.

Detailsinfo

A vulnerability has been found in sumatrapdfreader SumatraPDF up to 3.5.2 on Windows and classified as problematic. Affected by this vulnerability is an unknown code of the component Installer Handler. The manipulation with an unknown input leads to a certificate validation vulnerability. The CWE definition for the vulnerability is CWE-295. The product does not validate, or incorrectly validates, a certificate. As an impact it is known to affect integrity. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-25961 since 02/09/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. Technical details are unknown but a public exploit is available. The attack technique deployed by this issue is T1587.003 according to MITRE ATT&CK.

It is possible to download the exploit at exploit-db.com. It is declared as proof-of-concept.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at Exploit-DB (52535). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• sumatrapdfreader

Name

• SumatraPDF

Version

• 3.5.0
• 3.5.1
• 3.5.2

Website

• Product: https://github.com/sumatrapdfreader/sumatrapdf/

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Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

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