TI-2026-37883 Aliases CVE-2026-52767 GHSA-mv28-wj57-f57g

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

HIGH 75CWE-347Published 2026-09-04 · Updated 2026-09-08

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: Security bypass
Confidentiality · integrity · availability: None · High · Low
Fix status: Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-347.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00352 29th percentileScored 2026-11-07

Fix Fixed yeswiki (YesWiki): 4.6.6yeswiki/yeswiki (Packagist): 4.6.6

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
YesWiki	yeswiki	4.6.2 to before 4.6.6	4.6.6	Patch available	CNA
—	yeswiki/yeswiki (Packagist)	4.6.2 to before 4.6.6	4.6.6	Patch available	GHSA-mv28-wj57-f57g

yeswiki VendorYesWiki Affected 4.6.2 to before 4.6.6 Fixed in 4.6.6 Patch available CNA
yeswiki/yeswiki (Packagist) Vendor— Affected 4.6.2 to before 4.6.6 Fixed in 4.6.6 Patch available GHSA-mv28-wj57-f57g

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPE	Versions	Role	Vendor
cpe:2.3:a:yeswiki:yeswiki::::::::	—	—	YesWiki

cpe:2.3:a:yeswiki:yeswiki:*:*:*:*:*:*:*:* Versions — — ·YesWiki

Remediation

Fix · CNA yeswiki (YesWiki) Fixed in 4.6.6
Fix · GHSA-mv28-wj57-f57g yeswiki/yeswiki (Packagist) Fixed in 4.6.6 Advisory →

Timeline

2026-10-02 Threatist record created from CVE-2026-52767
2026-10-03 Alias added: GHSA-mv28-wj57-f57g

References

Other 4

TI-2026-37893 YesWiki has Unsafe eval() in Formula Calculator - Remote Code Execution (RCE) & Denial of Service (DoS) CVSS 3.1CRITICAL 9.8
TI-2026-34305 YesWiki: Unauthenticated SQL Injection CVSS 3.1CRITICAL 9.8
TI-2025-29089 YesWiki Vulnerable to Unauthenticated Site Backup Creation and Download CVSS 3.1CRITICAL 10.0
TI-2024-34399 Use of a Broken or Risky Cryptographic Algorithm in YesWiki CVSS 3.1CRITICAL 9.9
TI-2026-37882 YesWiki: Unauthenticated arbitrary page deletion via `{{erasespamedcomments}}` action CVSS 3.1CRITICAL 9.1
TI-2026-80227 SQL injection in YesWiki Bazar entry creation via date_maj_fiche CVSS 4.0HIGH 8.8

See all 85 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences