Executive brief
YesWiki, a collaborative wiki platform, contains a vulnerability in its ActivityPub integration that allows unauthorized outsiders to force the server to make web requests to arbitrary locations. This can be used to probe internal corporate networks, access private cloud configuration data, or scan for other vulnerable systems that are not normally accessible from the internet. An attacker does not need an account or special permissions to trigger this behavior if the ActivityPub feature is enabled.
Technical details
A Server-Side Request Forgery (SSRF) vulnerability exists in YesWiki's ActivityPub implementation, specifically within the `HttpSignatureService::verifySignature()` method. The application processes the `Signature` HTTP header from incoming POST requests to the `/api/forms/{formId}/actor/inbox` route. The `keyId` parameter, which is expected to be a URL pointing to a public key, is fetched via a GET request before any cryptographic verification or URL validation occurs. An unauthenticated remote attacker can provide an arbitrary URL (including internal IP addresses or cloud metadata services like 169.254.169.254) to perform internal port scanning or credential theft. The vulnerability is present when ActivityPub is enabled on at least one Bazar form. This issue is patched in version 4.6.6.
Affected products
- YesWiki yeswiki/yeswiki >= 4.6.2, < 4.6.6
Timeline
- 2026-06-02: disclosed
- 2026-07-09: advisory
- 2026-07-09: patched