CVE-2026-42180 Details
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.
A blind server-side request forgery (SSRF) vulnerability has been identified in Lemmy versions prior to 0.19.18. This issue allows an authenticated low-privileged user to exploit the Webmention feature by sending a link post to a public community. The vulnerability arises because the application does not properly validate the URL before dispatching the Webmention, allowing internal or loopback addresses to be targeted. As a result, an attacker can trigger server-side HTTP requests to internal services, potentially leading to unauthorized access or manipulation of internal resources.
Users are advised to update Lemmy to version 0.19.18 or later, where this vulnerability has been patched.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed May 8, 2026CISA-ADP
Assessed May 13, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948 | CISA-ADP | AdvisoryExploitRemedyVendor |
| https://github.com/LemmyNet/lemmy/releases/tag/0.19.18 | [email protected] | Release NotesVendor |
| https://github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948 | [email protected] | AdvisoryExploitRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-918 | Server-Side Request Forgery (SSRF) | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| Lemmy | 0.19.17 (semver) |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 13, 2026 | CVE Modified | CISA-ADP |
| May 8, 2026 | New CVE Received | [email protected] |