Vulnerability in Yeswiki
CVE-2026-52767
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L.
EPSS exploit prediction
EPSS: 0.004 (27.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 27th percentile — 27.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.001
Affected products
- Yeswiki — versions >= 4.6.2, < 4.6.6
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-52767?
- CVE-2026-52767 is a high-severity vulnerability in Yeswiki, classified under Improper Verification of Cryptographic Signature. CVSS score: 8.2/10. Published 2026-09-05.
- How severe is CVE-2026-52767?
- High severity. CVSS v3 base score is 8.2 out of 10.