CVE-2026-42181: Lemmynet Lemmy

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.19.18, Lemmy fetches metadata for user-supplied post URLs and, under the default StoreLinkPreviews image mode, downloads the preview image through local pict-rs. While the top-level page URL is checked against internal IP ranges, the extracted og:image URL is not subject to the same restriction. As a result, an authenticated low-privileged user can submit an attacker-controlled public page whose Open Graph image points to an internal image endpoint. Lemmy will fetch that internal image server-side and store a local thumbnail that can then be served back to users. This issue has been patched in version 0.19.18.

Affected products

• Lemmynet Lemmy: before 0.19.18 (fixed in 0.19.18)

Published 2026-05-08. Last modified 2026-06-17.