CVE-2026-54741
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.
References
- https://github.com/LemmyNet/lemmy/commit/051b317c9d14b91972bb372c67f319d6900beb93
- https://github.com/LemmyNet/lemmy/commit/2d169d630b86b9351e4b1dca451214b741f46150
- https://github.com/LemmyNet/lemmy/pull/6472
- https://github.com/LemmyNet/lemmy/pull/6476
- https://github.com/LemmyNet/lemmy/releases/tag/0.19.19