What’s Vulnerable › Vulnerabilities

CVE-2026-52767: YesWiki: Unauthenticated ActivityPub Signature-Verification Bypass via `!openssl_verify(...)` accepting `int(-1)`

• Severity: high (CVSS 8.2 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-05 · updated 2026-09-08
• Weakness: CWE-347

Description

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: from 4.6.2, < 4.6.6

References

• https://github.com/YesWiki/yeswiki/commit/d1795e0301e1a1078f17b4b98f56fff70de2029e
• https://github.com/YesWiki/yeswiki/releases/tag/v4.6.6
• https://github.com/YesWiki/yeswiki/security/advisories/GHSA-mv28-wj57-f57g
• https://github.com/YesWiki/yeswiki/security/advisories/GHSA-mv28-wj57-f57g

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