CVE-2026-54741: CWE-862: Missing Authorization in LemmyNet lemmy
Lemmy 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.
AI Analysis
Technical Summary
The vulnerability (CWE-862) in LemmyNet lemmy involves missing authorization checks in the edit_private_message function. Although create_private_message verifies the recipient's block list before allowing message creation, edit_private_message only verifies that the caller is the original message creator and does not re-check the recipient's block list. Consequently, a sender blocked by the recipient can still edit an existing private message, circumventing the block and enabling harassment. This issue is resolved in versions 0.19.19 and 1.0.0-alpha.18.
Potential Impact
An attacker who has been blocked by a recipient can continue to modify existing private messages visible to that recipient, bypassing the intended block. This allows continued harassment or unwanted communication despite the block. The vulnerability does not allow creating new messages post-block but permits editing of old messages.
Mitigation Recommendations
Upgrade LemmyNet lemmy to version 0.19.19 or later, or 1.0.0-alpha.18 or later, where this authorization check issue has been fixed. No other mitigations are indicated.
CVE-2026-54741: CWE-862: Missing Authorization in LemmyNet lemmy
Description
Lemmy 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.
CVSS v4.0
Score 5.3medium
Affected software
pkg:github/lemmynet/lemmyRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability (CWE-862) in LemmyNet lemmy involves missing authorization checks in the edit_private_message function. Although create_private_message verifies the recipient's block list before allowing message creation, edit_private_message only verifies that the caller is the original message creator and does not re-check the recipient's block list. Consequently, a sender blocked by the recipient can still edit an existing private message, circumventing the block and enabling harassment. This issue is resolved in versions 0.19.19 and 1.0.0-alpha.18.
Potential Impact
An attacker who has been blocked by a recipient can continue to modify existing private messages visible to that recipient, bypassing the intended block. This allows continued harassment or unwanted communication despite the block. The vulnerability does not allow creating new messages post-block but permits editing of old messages.
Mitigation Recommendations
Upgrade LemmyNet lemmy to version 0.19.19 or later, or 1.0.0-alpha.18 or later, where this authorization check issue has been fixed. No other mitigations are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-15T23:12:41.964Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a86e0f3acd9273b4983851a
Added to database: 08/20/2026, 11:11:47 UTC
Last enriched: 08/20/2026, 11:22:46 UTC
Last updated: 08/20/2026, 22:52:13 UTC
Views: 4
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