Vulnerability · Published May 8, 2026 · Assigned by GitHub_M
CVE-2026-42181Lemmy: SSRF and internal image disclosure in post link metadata via unvalidated og:image
Medium 6.5
In plain English
A medium-severity server-side request forgery in lemmy from LemmyNet. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities).
Official description
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 (as reported)
Weakness: CWE-918 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
References
- https://github.com/LemmyNet/lemmy/security/advisories/GHSA-h6hf-9846-xwrq x_refsource_CONFIRM
- https://github.com/LemmyNet/lemmy/releases/tag/0.19.18 x_refsource_MISC