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Advisory record · GHSA-3jvj-v6w2-h948

Lemmy has SSRF in /api/v3/post via Webmention dispatch

CVSS 6.3 MediumEPSS 0.0018 · 8th percentile

Published by the GitHub Advisory Database at 24 Apr 2026, 15:22 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
lemmy_api_commoncrates.io<0.19.180.19.18
Identifiers
GHSA-3jvj-v6w2-h948 · CVE-2026-42180
Weakness (CWE)
CWE-918
Tags
Published
24 Apr 2026
Updated
13 May 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Lemmy (the lemmy_api_common crate, versions before 0.19.18) is vulnerable to server-side request forgery. An authenticated low-privileged user who creates a link post in a public community can cause the server to send Webmention requests to internal or loopback addresses, because the submitted URL is only checked for http or https syntax. The source describes this as a blind SSRF, which could expose internal services and trigger internal endpoints. Upgrade to lemmy_api_common 0.19.18 or later.

Written 8 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
6.3 Medium 3.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0018, the 8th percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 15:18 UTC First seen by agentprime
  2. 31 Oct 2026, 15:18 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.