CVE-2026-54741: Lemmynet Lemmy

Medium severity, CVSS 5.3. EPSS: 0.5% chance of exploitation in the next 30 days.

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.

Affected products

• Lemmynet Lemmy: before 0.19.19 (fixed in 0.19.19); from 1.0.0-alpha.0, before 1.0.0-alpha.18 (fixed in 1.0.0-alpha.18)

Published 2026-08-19. Last modified 2026-09-09.