Lemmy has SSRF and internal image disclosure in post link metadata via unvalidated og:image

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-42181: 0.26% estimated exploitation activity in the next 30 days; percentile 18.28 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details The metadata fetch logic applies an internal-address check only to the initial post URL. After HTML parsing, extractopengraphdata() accepts absolute og:image values and returns them as-is. Later, generatepostlinkmetadata() passes that second-hop image URL into generatepictrsthumbnail(), which instructs local pict-rs to fetch it through image/download?url=.... This creates a two-stage source-to-sink chain where the…

Published by the source

24 Apr 2026, 15:21 UTC

Last modified by the source

13 May 2026, 13:34 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-h6hf-9846-xwrq

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# Patch Next advisory brief: CVE-2026-42181

Advisory: Lemmy has SSRF and internal image disclosure in post link metadata via unvalidated og:image
IDs: CVE-2026-42181, GHSA-h6hf-9846-xwrq
Record: https://patchnext.com/advisories/cve-2026-42181 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lemmy_api_common 0.19.18. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io lemmy_api_common: affected < 0.19.18; fixed in 0.19.18

## Suggested inspection (read-only)
- crates.io lemmy_api_common: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on lemmy_api_common.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-h6hf-9846-xwrq (GitHub-reviewed advisory GHSA-h6hf-9846-xwrq lists affected ranges: crates.io lemmy_api_common >=0 <0.19.18)

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