CVE-2026-52767

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

Published Sep 4, 2026 CVSS 3.1 · 8.2 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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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)`
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Yeswiki
Yeswiki yeswiki
Vendors & Products Yeswiki
Yeswiki yeswiki
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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Sep 8, 2026, 6:02 PM
Reserved
Jun 8, 2026, 5:13 PM
Status
Deferred
Published
Sep 5, 2026, 12:17 AM
Modified
Sep 8, 2026, 9:05 PM