Executive brief
YesWiki, a collaborative wiki platform, contains a security flaw in its Bazar form field calculator. This component allows users to create mathematical formulas, but it fails to safely process these inputs. An attacker can exploit this to either crash the web server, causing a service outage, or execute malicious commands to steal sensitive data and take control of the system.
Technical details
A code injection vulnerability exists in YesWiki's Bazar form field calculator (CalcField.php) within the formatValuesBeforeSave method. The application uses a complex recursive regular expression to validate user-defined formulas before passing them to the PHP eval() function. This implementation is susceptible to Regular Expression Denial of Service (ReDoS) via stack overflow in the PCRE engine, leading to a segmentation fault and service crash. Furthermore, if the regex validation is bypassed, an attacker can achieve arbitrary PHP code execution with the privileges of the web server user. The vulnerability is patched in version 4.6.6 by replacing eval() with a safer parsing mechanism.
Affected products
- YesWiki YesWiki < 4.6.6
Timeline
- 2026-06-02: patched: Version 4.6.6 released
- 2026-06-08: advisory: NVD published CVE-2026-52778
- 2026-07-09: advisory: GitHub Advisory published