Server-Side Request Forgery Vulnerability in Lemmy Link Aggregator
CVE-2026-42180

6.3MEDIUM

Key Information:

Vendor

Lemmynet

Status
Lemmy
Vendor
CVE Published:
8 May 2026

What is CVE-2026-42180?

A vulnerability in Lemmy, a link aggregator for the fediverse, allows authenticated low-privileged users to create a link post through the POST /api/v3/post endpoint. When a post is made in a public community, the system asynchronously sends a Webmention request to an attacker-controlled link, without properly rejecting loopback or private addresses. This oversight enables a regular user to trigger server-side HTTP requests to internal services. The issue was addressed in version 0.19.18.

Affected Version(s)

lemmy < 0.19.18

References

https://github.com/LemmyNet/lemmy/security/advisories/GHS...
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https://github.com/LemmyNet/lemmy/releases/tag/0.19.18
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CVSS V3.1

Score:
6.3
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
Low
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.