Executive Summary

CVE-2026-8931 is a critical Remote Code Execution (RCE) vulnerability found in older versions (2.0.3 through 2.5.3) of the Disig Web Signer application, which runs on Windows, macOS, and Linux.

This vulnerability allows an attacker to execute arbitrary code remotely, potentially compromising the affected system.

The issue was discovered by security expert Marek Alakša from Binary House and has been fixed in version 2.5.5 of the Web Signer application.

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Impact Analysis

This critical Remote Code Execution vulnerability can allow attackers to run malicious code on your system without your permission.

Such an exploit could lead to unauthorized access, data theft, system compromise, or further attacks within your network.

Because the vulnerability affects a widely used digital signing application, it poses a significant security risk to users who have not updated to the fixed version.

Immediate updating to version 2.5.5 is strongly recommended to mitigate these risks.

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Detection Guidance

This vulnerability affects Disig Web Signer versions 2.0.3 through 2.5.3. Detection can be done by verifying the installed version of the Web Signer application on your system.

To detect if your system is vulnerable, check the version of the Web Signer application installed on your Windows, macOS, or Linux system. If the version is between 2.0.3 and 2.5.3 inclusive, the system is vulnerable.

Suggested commands to check the installed version depend on the operating system:

• On Windows, check the application version via the Control Panel's Programs and Features or by right-clicking the Web Signer executable and viewing Properties > Details.
• On macOS, use the Finder to locate the Web Signer app, then use 'Get Info' to see the version, or run a command in Terminal such as: `/Applications/WebSigner.app/Contents/MacOS/WebSigner --version` if supported.
• On Linux, check the version by running a command like: `websigner --version` or check the package manager, e.g., `dpkg -l | grep websigner` or `rpm -qa | grep websigner`.

Since the vulnerability is specific to versions 2.0.3 through 2.5.3, confirming the installed version within this range indicates exposure.

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Mitigation Strategies

The primary and immediate mitigation step is to update the Disig Web Signer application to the latest version, 2.5.5, which contains the fix for this critical vulnerability.

Users can update either through an automatic prompt from the application or manually by checking for updates via the system tray icon.

Alternatively, updated installation packages are available for download on the official Disig website, which can be used to perform a manual update.

Prompt action is strongly recommended to ensure protection against potential exploitation of this critical Remote Code Execution vulnerability.

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