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Server-Side Request Forgery (SSRF)Weakness · CWE-918

CVE-2026-42181

MEDIUM · 6.5 CVSS v3.1 Published 2026-05-08
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Lemmy fails to validate og:image URLs against internal IP range restrictions, unlike the top-level URL. An authenticated low-privileged user can supply a URL with an internal og:image, causing the server to fetch and store internal resources (SSRF).

MitigationUpgrade to Lemmy version 0.19.18 or later which patches the og:image URL validation to also check against internal IP ranges.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Lemmy installation
    Locate the Lemmy instance - typically runs as a Rust binary, Docker container, or behind a reverse proxy. Check running processes or container logs for 'lemmy' references.
    Affected if Lemmy software is present in the environment
  2. Determine installed Lemmy version
    Check the version by querying the instance API at /api/v3/site, reviewing Docker image tags, or running 'lemmy --version' if CLI access is available. Compare against the patched version 0.19.18.
    Affected if Installed version is lower than 0.19.18 (e.g., 0.19.17, 0.19.16, etc.)
  3. Verify low-privileged user access to post creation
    Confirm that authenticated users with standard (non-admin) privileges can create or edit posts. The vulnerability requires a user to supply an og:image URL in a post.
    Affected if Standard users can create or modify posts containing custom og:image URLs
  4. Check network accessibility to internal resources
    Assess whether the Lemmy server can reach internal IP ranges (127.0.0.0/8, 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) from its network position. Review firewall rules and network topology.
    Affected if The server can initiate outbound HTTP/HTTPS connections to internal IP addresses

A user is affected if running Lemmy version below 0.19.18 where low-privileged users can embed og:image URLs in posts and the server can reach internal network resources.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to Lemmy version 0.19.18 or later which patches the og:image URL validation to also check against internal IP ranges.

Recommended fix High confidence

Lemmy version 0.19.18 or later

  1. 1. Identify the current Lemmy version currently running in your environment.
  2. 2. Plan an upgrade to Lemmy version 0.19.18 or later.
  3. 3. Before upgrading, review the Lemmy release notes for version 0.19.18 to confirm the SSRF vulnerability fix is included.
  4. 4. Perform the upgrade following standard Lemmy upgrade procedures (typically involves pulling the latest Docker image or updating the package).
  5. 5. After upgrading, verify that the pict-rs image fetching now properly validates og:image URLs against internal IP ranges.
  6. 6. Consider reviewing logs to ensure no exploitation attempts occurred prior to the upgrade.

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA4.0 h
20.0 hours of engineering $3,560
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42181 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data