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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.2 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L

EPSS

• CVE-2026-52767: 0.35% estimated exploitation activity in the next 30 days; percentile 28.93 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary HttpSignatureService::verifySignature() checks the result of PHP's opensslverify() with a loose boolean negation - if (!opensslverify(...)) { throw ... }. PHP's opensslverify has four possible return values: | return | meaning | !return | | ------ | ------------------------------------------------ | --------- | | 1 | signature is valid | false | | 0 | signature is invalid | true ✓ | | -1 | the verify call itself failed (internal error) | false ❌ | | false| input rejected by PHP's argument validation | true ✓ | 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 EVPVerifyFinal() return -1 triggers the bypass. The two practical paths to -1 we are aware of: 1. DSA / EC public key with an RSA-only algorithm. opensslverify(..., $dsaKey, "RSA-SHA256") returns int(-1) on PHP 8.3 + OpenSSL 3.x. This is the path the PoC uses; it works…

Published by the source

9 Jul 2026, 20:58 UTC

Last modified by the source

9 Jul 2026, 20:58 UTC

Source last checked

26 Oct 2026, 14:50 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-mv28-wj57-f57g

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# Patch Next advisory brief: CVE-2026-52767

Advisory: YesWiki Vulnerable to Unauthenticated ActivityPub Signature-Verification Bypass via `!openssl_verify(...)` accepting `int(-1)`
IDs: CVE-2026-52767, GHSA-mv28-wj57-f57g
Record: https://patchnext.com/advisories/cve-2026-52767 (revision 1, source checked 26 Oct 2026, 14:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: yeswiki/yeswiki 4.6.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist yeswiki/yeswiki: affected >= 4.6.2, < 4.6.6; fixed in 4.6.6

## Suggested inspection (read-only)
- Packagist yeswiki/yeswiki: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on yeswiki/yeswiki.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-mv28-wj57-f57g (GitHub-reviewed advisory GHSA-mv28-wj57-f57g lists affected ranges: Packagist yeswiki/yeswiki >=4.6.2 <4.6.6)

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