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.

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact High

Availability Impact Low

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
YesWiki yeswiki affected
Version Status Constraints
>= 4.6.2, < 4.6.6 affected —

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Project Subscriptions

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-mv28-wj57-f57g YesWiki Vulnerable to Unauthenticated ActivityPub Signature-Verification Bypass via `!openssl_verify(...)` accepting `int(-1)`
Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/YesWiki/yeswiki/commit/d1795e0301e1a1078f17b4b98f56fff70de2029e cve-icon cve-icon
https://github.com/YesWiki/yeswiki/releases/tag/v4.6.6 cve-icon cve-icon
https://github.com/YesWiki/yeswiki/security/advisories/GHSA-mv28-wj57-f57g cve-icon cve-icon
History

Fri, 04 Sep 2026 23:45:00 +0000

Type Values Removed Values Added
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.
Title YesWiki: Unauthenticated ActivityPub Signature-Verification Bypass via `!openssl_verify(...)` accepting `int(-1)`
Weaknesses CWE-347
References
Metrics cvssV3_1

{'score': 8.2, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-09-04T23:40:39.725Z

Reserved: 2026-06-08T17:13:43.064Z

Link: CVE-2026-52767

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-05T00:17:19.540

Modified: 2026-09-05T00:17:19.540

Link: CVE-2026-52767

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-05T00:30:18Z

Weaknesses