---
cve: "CVE-2026-54740"
severity: "MEDIUM"
cvss: 6.5
epss: "31%"
vendor: "LemmyNet"
kev: false
exploited: false
published: "2026-08-19 20:14:29"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-09-07T07:26:20+02:00"
---

# CVE-2026-54740

> 6.5 MEDIUM · 🧪 PoC

## Beschreibung

Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-alpha.18, a lower-ranked remote moderator can remove a higher-ranked moderator by sending a signed ActivityPub Remove activity to the target instance. The local API uses LocalUser::is_higher_mod_or_admin_check to enforce moderator rank, but CollectionRemove::verify in crates/apub/activities/src/community/collection_remove.rs only calls verify_mod_action. CollectionRemove::receive dereferences self.object as an ApubPerson, creates a CommunityModeratorForm, and calls CommunityActions::leave without checking that the actor outranks the moderator identified by the object field. In communities with federated moderators, a junior moderator can therefore strip senior moderators from the community moderator list even though the local API rejects the same action. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.

## CVSS-Vektor

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

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Gering | warn |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Keine | good |
| I Integrität | Hoch | bad |
| A Verfügbarkeit | Keine | good |

## Patch verfügbar (OSV)

- f6e986e7e54d456aa1ffec38f1576c5bb15e0afd (Commit)
- 0ab1cd744b659d0f5e35b77dbded142bed550487 (Commit)

## Referenzen

- <https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7>
- <https://github.com/LemmyNet/lemmy/pull/6475>
- <https://github.com/LemmyNet/lemmy/pull/6478>
- <https://github.com/LemmyNet/lemmy/commit/d127e714a66f34f6b9c8ea15f20097ac907cdf28>
- <https://github.com/LemmyNet/lemmy/commit/ede1d348344ca2027fd1bc6a0cab25575c0c3a4c>
- <https://github.com/LemmyNet/lemmy/releases/tag/0.19.19>
- <https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.18>
- <https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-54740) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_