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

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Summary

CVECVE-2026-42181
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-08 20:16:31 UTC
Updated2026-05-12 15:31:36 UTC
DescriptionLemmy 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

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

EPSS: 0.000280000 probability, percentile 0.081430000 (date 2026-05-12)

Problem Types: CWE-918 | CWE-918 CWE-918: Server-Side Request Forgery (SSRF)

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
3.1CNADECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA LemmyNet Lemmy affected < 0.19.18 Not specified

References

ReferenceSourceLinkTags
github.com/LemmyNet/lemmy/releases/tag/0.19.18 [email protected] github.com
github.com/LemmyNet/lemmy/security/advisories/GHSA-h6hf-9846-xwrq 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
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