yeswiki up to 4.6.5 Regular Expression CalcField.php eval code injection

Summaryinfo

A vulnerability categorized as critical has been discovered in yeswiki up to 4.6.5. Impacted is the function eval of the file CalcField.php of the component Regular Expression Handler. Executing a manipulation can lead to code injection. This vulnerability is handled as CVE-2026-52778. The attack can be executed remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in yeswiki up to 4.6.5. It has been declared as critical. This vulnerability affects the function eval of the file CalcField.php of the component Regular Expression Handler. The manipulation with an unknown input leads to a code injection vulnerability. The CWE definition for the vulnerability is CWE-94. The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

YesWiki is a wiki system written in PHP. Prior to version 4.6.6, an unsafe execution vulnerability exists in the Bazar form field calculator (CalcField.php) of YesWiki. The application attempts to sanitize user-defined mathematical formulas using a complex recursive regular expression before passing them to the PHP eval() function. This implementation is inherently flawed: it is vulnerable to Regular Expression Denial of Service (ReDoS / Stack Overflow) which can crash the server, and it creates a high-risk architecture where any logic bypass directly results in arbitrary PHP code execution. Version 4.6.6 patches the issue.

The advisory is available at github.com. This vulnerability was named CVE-2026-52778 since 06/08/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1059 by the MITRE ATT&CK project.

By approaching the search of inurl:CalcField.php it is possible to find vulnerable targets with Google Hacking.

Upgrading to version 4.6.6 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch dd2bd8fb099de0d21504bda8a810693b3fcb8e52 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Content Management System

Name

• yeswiki

Version

• 4.6.0
• 4.6.1
• 4.6.2
• 4.6.3
• 4.6.4
• 4.6.5

License

• open-source

Website

• Product: https://github.com/YesWiki/yeswiki/

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