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

Quick assessment

Affected
LemmyNet lemmy
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

LemmyNet lemmy是LemmyNet组织的一个去中心化的链接聚合与讨论社区平台。 LemmyNet lemmy 0.19.19之前版本和1.0.0-alpha.20之前版本存在授权问题漏洞，该漏洞源于未验证帖子所属社区，导致社区版主可通过联邦CollectionAdd和CollectionRemove活动将其他社区的帖子置顶或取消置顶，或撤销其他社区的策展决定。

CVSS 5.1 · Medium EPSS 0.42% · P35

Possible ATT&CK Techniques 1 AI

T1098 · Account Manipulation

Affected Version Matrix 2

VendorProduct Version RangeStatus
LemmyNet lemmy < 0.19.19 affected
>= 1.0.0-alpha.0, < 1.0.0-alpha.20 affected
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I. Basic Information for CVE-2026-54742

Vulnerability Information
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Vulnerability Title
Lemmy: `CollectionAdd::Featured` does not check the post is in the community
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制不正确
Source: CVE Program / CVE List V5
Vulnerability Title
LemmyNet lemmy 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
LemmyNet lemmy是LemmyNet组织的一个去中心化的链接聚合与讨论社区平台。 LemmyNet lemmy 0.19.19之前版本和1.0.0-alpha.20之前版本存在授权问题漏洞，该漏洞源于未验证帖子所属社区，导致社区版主可通过联邦CollectionAdd和CollectionRemove活动将其他社区的帖子置顶或取消置顶，或撤销其他社区的策展决定。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
LemmyNet lemmy < 0.19.19 -

II. Public POCs for CVE-2026-54742

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III. Intelligence Information for CVE-2026-54742

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Patches & Fixes for CVE-2026-54742 (2)

Vendor Advisories for CVE-2026-54742 (1)

Vendor Pages for CVE-2026-54742 (3)

Same Patch Batch · LemmyNet · 2026-08-19 · 6 CVEs total

CVE-2026-54739 6.9 MEDIUM Lemmy: Login Endpoint User Enumeration via HTTP Response Code Differential
CVE-2026-54740 6.5 MEDIUM Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators
CVE-2026-54738 6.5 MEDIUM Lemmy: Rate limit bypass via X-Forwarded-For header spoofing in actix-web ConnectionInfo
CVE-2026-54743 6.4 MEDIUM Lemmy: Stored XSS via markdown image alt-text in lemmy-ui html5-embed
CVE-2026-54741 5.3 MEDIUM Lemmy: Blocked users can edit private messages sent before the block

IV. Related Vulnerabilities

Same product: lemmy
Same vendor: LemmyNet
Same weakness: CWE-863

V. Comments for CVE-2026-54742

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