Quick answers
- Is This vulnerability exploited in the wild?
- No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
- How severe is This vulnerability?
- Medium severity, with a CVSS score of 5.3, published 6 May 2026.
- Which products and versions are affected?
- lemmy_api (crates.io) <= 0.19.1-rc.1.
- Is there a fix for This vulnerability?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is This vulnerability attacked?
- It is attacked over the network, in a hosted service.
- Am I affected?
- Check whether you run lemmy_api (crates.io) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A missing authorization check in the `read_multi_community()` function allows unauthenticated users to bypass the `private_instance` configuration. While other read handlers (such as those for posts, comments, and searches) correctly call `check_private_instance()`, this specific endpoint does not. An attacker can exploit this via a simple GET request to `/multi_community` to retrieve sensitive metadata including community names, titles, summaries, sidebars, owner identities, and member community lists. This vulnerability primarily affects development versions up to 0.19.1-rc.1.
Affected products
- LemmyNet lemmy_api <= 0.19.1-rc.1
Timeline
- 2026-04-29: disclosed: Vulnerability reported to LemmyNet
- 2026-05-06: advisory: GitHub Advisory published