CVE-2026-54742
Lemmy: `CollectionAdd::Featured` does not check the post is in the community
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.
INFO
Published Date :
Aug. 19, 2026, 8:17 p.m.
Last Modified :
Aug. 19, 2026, 8:17 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-54742
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 4.0 | MEDIUM | [email protected] |
Solution
- Update Lemmy to version 0.19.19.
- Update Lemmy to version 1.0.0-alpha.20.
- Ensure moderators are authorized for actions.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-54742.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-54742 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-54742
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-54742 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-54742 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Aug. 19, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'LemmyNet', 'product': 'lemmy', 'versions': [{'status': 'affected', 'version': '< 0.19.19'}, {'status': 'affected', 'version': '>= 1.0.0-alpha.0, < 1.0.0-alpha.20'}]}] Added 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. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-863 Added Reference https://github.com/LemmyNet/lemmy/commit/108d78c592cc88bac2b0bf52ca6631be54f6fb23 Added Reference https://github.com/LemmyNet/lemmy/commit/abe256243822526dcd4bca857f7c0adeb49944f5 Added Reference https://github.com/LemmyNet/lemmy/pull/6500 Added Reference https://github.com/LemmyNet/lemmy/pull/6501 Added Reference https://github.com/LemmyNet/lemmy/releases/tag/0.19.19 Added Reference https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.20 Added Reference https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v Added Reference https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19