CVE-2026-42180 — Lemmy is a link aggregator and forum for the fediverse.
CVE-2026-42180 — 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 att
What This Means For You
- If your environment is affected by CWE-918, review your exposure and prioritize patching based on your environment. Monitor vendor advisories for CVE-2026-42180 updates and patches.
Related ATT&CK Techniques
🛡️ Detection Rules
3 rules · 6 SIEM formats3 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
CVE-2026-42180 - Lemmy Unauthenticated SSRF via Webmention
title: CVE-2026-42180 - Lemmy Unauthenticated SSRF via Webmention
id: scw-2026-05-08-ai-1
status: experimental
level: critical
description: |
Detects the specific API endpoint and method used by CVE-2026-42180 to create a link post. This allows an authenticated low-privileged user to trigger server-side HTTP requests to internal services by submitting a crafted URL in a post. This rule specifically targets the vulnerable POST request to /api/v3/post.
author: SCW Feed Engine (AI-generated)
date: 2026-05-08
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-42180/
tags:
- attack.initial_access
- attack.t1190
logsource:
category: webserver
detection:
selection:
cs-uri|endswith:
- '/api/v3/post'
cs-method:
- 'POST'
condition: selection
falsepositives:
- Legitimate administrative activity
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-42180 | vulnerability | CVE-2026-42180 |
| CWE-918 | weakness | CWE-918 |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 08, 2026 at 23:16 UTC |
This content was curated and summarized by Shimi's Cyber World for informational purposes. It is not copied or republished in full. All intellectual property rights remain with the original author and source.
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