CVE-2026-52767

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CVE-2026-52767

Summary: YesWiki: Unauthenticated ActivityPub Signature-Verification Bypass via `!openssl_verify(...)` accepting `int(-1)`

Details: 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.

References: https://github.com/YesWiki/yeswiki/releases/tag/v4.6.6, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52767.json, https://github.com/YesWiki/yeswiki/security/advisories/GHSA-mv28-wj57-f57g, https://nvd.nist.gov/vuln/detail/CVE-2026-52767, https://github.com/YesWiki/yeswiki/commit/d1795e0301e1a1078f17b4b98f56fff70de2029e