# CVE-2026-54742: Lemmy: `CollectionAdd::Featured` does not check the post is in the community

> Community moderators can feature or unfeature posts in other communities by bypassing ownership checks, allowing unauthorized modification of community content listings.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 19 Aug 2026
- **Updated:** 20 Aug 2026
- **Also known as:** GHSA-gwfj-h8r7-792v

## What is CVE-2026-54742?

CVE-2026-54742 is a medium-severity missing authorization vulnerability in LemmyNet lemmy, published on 19 Aug 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Lemmy is a link aggregator and forum for the fediverse. From 0.19.18 until 0.19.19 and 1.0.0-alpha.20, a community moderator can feature or unfeature posts in other communities through federated CollectionAdd and CollectionRemove activities using CollectionType::Featured. After verify_mod_action authorizes the actor against self.community(), the receive handlers in crates/apub/activities/src/community/collection_add.rs and crates/apub/activities/src/community/collection_remove.rs dereference self.object as an ApubPost and update featured_community without verifying that post.community_id equals community.id. A moderator can therefore target an unrelated post owned by another community, push it into featured feeds and listings, or undo another community's legitimate curation decision. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.20.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-54742?


## How do I fix CVE-2026-54742?

No fix has been published for CVE-2026-54742 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-54742 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54742 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54742 and fix it if it is affected.

What it is: CVE-2026-54742 is a medium-severity missing authorization vulnerability in LemmyNet lemmy, published on 19 Aug 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54742 exists.

Affected product: LemmyNet lemmy. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-54742/ (Markdown: https://insights.sbomify.com/CVE-2026-54742/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54742
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54742
- OSV: https://osv.dev/vulnerability/CVE-2026-54742

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54742/
Summaries are generated and may contain mistakes; the official description above is the record.