CVE-2026-42180
Description
Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.19.18, Lemmy allows an authenticated low-privileged user to create a link post through POST /api/v3/post. When a post is created in a public community, the backend asynchronously sends a Webmention to the attacker-controlled link target. The submitted URL is checked for syntax and scheme, but the audited code path does not reject loopback, private, or link-local destinations before the Webmention request is issued. This lets a normal user trigger server-side HTTP requests toward internal services. This issue has been patched in version 0.19.18.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
lemmy_api_commoncrates.io | < 0.19.18 | 0.19.18 |
Affected products
1Patches
Vulnerability mechanics
References
5- github.com/advisories/GHSA-3jvj-v6w2-h948ghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-42180ghsaADVISORY
- github.com/LemmyNet/lemmy/commit/1f06693b708020c5c3a3752bd2f1c6006a75e9bcghsaWEB
- github.com/LemmyNet/lemmy/releases/tag/0.19.18nvdWEB
- github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948nvdWEB
News mentions
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