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Fencer Vulns
medium 6.5

CVE-2026-42181 json

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

published 2026-04-24 6 mo ago modified 2026-10-26 13 d ago also EUVD-2026-28820 , GHSA-h6hf-9846-xwrq

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 18%
public exploits
0
none known

Summary

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.

Patch / fix

  • crates.io lemmy_api_common 0.19.18
  • join-lemmy lemmy 0.19.18

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 18% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/LemmyNet/lemmy/security/advisories/GHSA-h6hf-9846-xwrq referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
crates.io lemmy_api_common
<0.19.18
0.19.18

Affected products

  • LemmyNet lemmy

Classification

Weakness
  • CWE-918 Server-Side Request Forgery

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.