Threat Intelligence Database

CVE-2026-54739 is a vulnerability in LemmyNet's lemmy software where the login endpoint reveals whether a username or email exists by returning different error responses. This discrepancy allows unauthenticated attackers to enumerate valid accounts, facilitating targeted credential attacks or social engineering. The issue affects versions prior to 0.19.19 and versions from 1.0.0-alpha.0 up to but excluding 1.0.0-beta.1. It is fixed in versions 0.19.19 and 1.0.0-beta.1.

CVE-2026-54740 is a missing authorization vulnerability in LemmyNet's lemmy software that allows a lower-ranked remote moderator to remove a higher-ranked moderator in federated communities. This occurs because the verification logic for moderator removal does not properly check the actor's rank against the target moderator's rank. The issue affects versions prior to 0.19.19 and 1.0.0-alpha.18 and has been fixed in those versions.

CVE-2026-54741 is a missing authorization vulnerability in LemmyNet's lemmy software that allows blocked senders to edit private messages after being blocked by the recipient. The create_private_message function properly checks the recipient's block list before allowing message creation, but the edit_private_message function does not perform this check. This flaw enables a blocked sender to modify existing messages visible to the recipient, potentially facilitating harassment. The issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.

Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.19.18, Lemmy allows an authenticated low-privileged user to create a link post through POST /api/v3/post. When a post is created in a public community, the backend asynchronously sends a Webmention to the attacker-controlled link target. The submitted URL is checked for syntax and scheme, but the audited code path does not reject loopback, private, or link-local destinations before the Webmention request is issued. This lets a normal user trigger server-side HTTP requests toward internal services. This issue has been patched in version 0.19.18.