CVE-2026-52767: Yeswiki

High severity, CVSS 8.2. EPSS: 0.4% chance of exploitation in the next 30 days.

YesWiki is a wiki system written in PHP. From version 4.6.2 to before version 4.6.6, HttpSignatureService::verifySignature() checks the result of PHP's openssl_verify() with a loose boolean negation - if (!openssl_verify(...)) { throw ... }. PHP's openssl_verify has four possible return values: 1, 0, -1, and "false". The -1 row is the bypass: PHP's truthiness rules make -1 a truthy value, so !(-1) === false, the throw is skipped, and the controller proceeds to processActivity(). Any condition that makes OpenSSL's EVP_VerifyFinal() return -1 triggers the bypass. The reachable consequence is the controller silently treats a failed verification as success and processes the attacker's payload. This issue has been patched in version 4.6.6.

Affected products

• Yeswiki Yeswiki: from 4.6.2, before 4.6.6 (fixed in 4.6.6)

Published 2026-09-05. Last modified 2026-09-08.