LemmyNet lemmy up to 0.19.17 Internal Image server-side request forgery

Summaryinfo

A vulnerability was found in LemmyNet lemmy up to 0.19.17. It has been classified as critical. This affects an unknown part of the component Internal Image Handler. This manipulation causes server-side request forgery. This vulnerability appears as CVE-2026-42181. The attack may be initiated remotely. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in LemmyNet lemmy up to 0.19.17 and classified as critical. Affected by this vulnerability is an unknown code block of the component Internal Image Handler. The manipulation with an unknown input leads to a server-side request forgery vulnerability. The CWE definition for the vulnerability is CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-42181 since 04/25/2026. The exploitation appears to be easy. The attack can be launched remotely. Neither technical details nor an exploit are publicly available.

Upgrading to version 0.19.18 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• LemmyNet

Name

• lemmy

Version

• 0.19.0
• 0.19.1
• 0.19.2
• 0.19.3
• 0.19.4
• 0.19.5
• 0.19.6
• 0.19.7
• 0.19.8
• 0.19.9
• 0.19.10
• 0.19.11
• 0.19.12
• 0.19.13
• 0.19.14
• 0.19.15
• 0.19.16
• 0.19.17

Website

• Product: https://github.com/LemmyNet/lemmy/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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