Lemmy: Blocked users can edit private messages sent before the block

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-54741
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-19 21:16:58 UTC
Updated2026-08-20 14:17:14 UTC
DescriptionLemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-alpha.18, Lemmy blocks new private messages from a sender after the recipient blocks that sender, but the edit path skips the same block check. create_private_message checks the recipient's block list with PersonActions::read_block before inserting a message, while edit_private_message in crates/api/api_crud/src/private_message/update.rs only checks that the caller is orig_private_message.creator_id. The update then writes new content and returns the modified PrivateMessageView without consulting the recipient's block list, allowing a blocked sender to keep changing an old message that the recipient can still see and providing a post-block harassment path. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.

Risk And Classification

Primary CVSS: v4.0 5.3 MEDIUM from [email protected]

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/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

EPSS: 0.003540000 probability, percentile 0.287140000 (date 2026-08-23)

Problem Types: CWE-862 | CWE-862 CWE-862: Missing Authorization

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary5.3MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED5.3MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
Low
User Interaction
None
Confidentiality
None
Integrity
Low
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA LemmyNet Lemmy affected < 0.19.19 Not specified
CNA LemmyNet Lemmy affected >= 1.0.0-alpha.0, < 1.0.0-alpha.18 Not specified

References

ReferenceSourceLinkTags
github.com/LemmyNet/lemmy/commit/2d169d630b86b9351e4b1dca451214b741f46150 [email protected] github.com
github.com/LemmyNet/lemmy/commit/051b317c9d14b91972bb372c67f319d6900beb93 [email protected] github.com
github.com/LemmyNet/lemmy/security/advisories/GHSA-46g9-847m-qf8r 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.18 [email protected] github.com
github.com/LemmyNet/lemmy/pull/6476 [email protected] github.com
github.com/LemmyNet/lemmy/releases/tag/0.19.19 [email protected] github.com
github.com/LemmyNet/lemmy/pull/6472 [email protected] github.com
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