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CVE-2026-54740— Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators

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.18之前版本存在授权问题漏洞，该漏洞源于CollectionRemove::verify仅调用verify_mod_action，未检查操作者是否高于被移除版主，可能导致低级别远程版主移除高级别版主。

CVSS 6.5 · Medium EPSS 0.43% · P36

Possible ATT&CK Techniques 1 AI

T1078 · Valid Accounts

Affected Version Matrix 2

VendorProduct Version RangeStatus
LemmyNet lemmy < 0.19.19 affected
>= 1.0.0-alpha.0, < 1.0.0-alpha.18 affected
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I. Basic Information for CVE-2026-54740

Vulnerability Information
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Vulnerability Title
Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制缺失
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.18之前版本存在授权问题漏洞，该漏洞源于CollectionRemove::verify仅调用verify_mod_action，未检查操作者是否高于被移除版主，可能导致低级别远程版主移除高级别版主。
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-2026-54740

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III. Intelligence Information for CVE-2026-54740

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Patches & Fixes for CVE-2026-54740 (4)

Vendor Advisories for CVE-2026-54740 (1)

Vendor Pages for CVE-2026-54740 (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-2026-54738 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
CVE-2026-54742 5.1 MEDIUM Lemmy: `CollectionAdd::Featured` does not check the post is in the community

IV. Related Vulnerabilities

Same product: lemmy
Same vendor: LemmyNet
Same weakness: CWE-862

V. Comments for CVE-2026-54740

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