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CVE-2026-52769 – Unauthenticated SSRF – YesWiki 4.6.2 to 4.6.5

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Summary

CVE-2026-52769 is an unauthenticated Server-Side Request Forgery (SSRF) vulnerability in YesWiki, a PHP-based collaborative wiki platform. The flaw resides in the ActivityPub inbox endpoint used by the Bazar tool, where an attacker-supplied URL is fetched by the server before any validation takes place. The issue carries a CVSS v3.1 base score of 8.3 (High) and requires no authentication or user interaction to exploit.

Technical details

  • Root cause: The HttpSignatureService::verifySignature() method (tools/bazar/services/HttpSignatureService.php, line 96) parses the HTTP Signature request header and extracts its keyId parameter, treating it as a URL. It immediately issues a server-side HTTP GET request to that URL before performing any cryptographic signature verification or URL/host validation.
  • Trigger conditions: The vulnerable code path is reached via the publicly accessible route POST /api/forms/{formId}/actor/inbox (defined in tools/bazar/controllers/ApiController.php, line 125), which is exposed with public ACL. Exploitation requires that ActivityPub is enabled on at least one Bazar form (bn_activitypub_enable = '1').
  • Attack vector: Network — an unauthenticated remote attacker sends a crafted request with a malicious Signature header containing an attacker-controlled keyId URL.
  • Impact: The server can be coerced into issuing arbitrary outbound HTTP requests to hosts it can reach, including internal-only services, cloud instance metadata endpoints (e.g., 169.254.169.254), and intranet admin panels. Response timing and error messages can be used as an oracle to enumerate internal services, scan ports, and potentially retrieve cloud IAM metadata.

Affected software

  • YesWiki versions from 4.6.2 up to and including 4.6.5

Severity

  • CVSS v3.1 Base Score: 8.3 (High)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

Mitigation and recommended actions

  • Immediate: Upgrade to YesWiki version 4.6.6 or later, which patches the signature verification flow.
  • If immediate patching is not possible: Disable ActivityPub on all Bazar forms (ensure bn_activitypub_enable is not set to '1') to remove the reachable code path, and restrict or block public access to the /api/forms/{formId}/actor/inbox endpoint at the network/WAF layer until the upgrade can be applied.

References

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