Vulnerability · Published Sep 4, 2026 · Assigned by GitHub_M

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

High 8.2

In plain English

A high-severity security flaw in yeswiki from YesWiki. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 29% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)8.2High

Exploit odds (30 days)0.4%top 71.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Packagist	yeswiki/yeswiki	4.6.6	GHSA-mv28-wj57-f57g

Affected products (as reported)

Vendor	Product	Versions
YesWiki	yeswiki	>= 4.6.2, < 4.6.6

Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L

References

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