CVE-2026-42180: CWE-918: Server-Side Request Forgery (SSRF) in LemmyNet lemmy
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 Analysis
Technical Summary
LemmyNet's lemmy software before version 0.19.18 contains an SSRF vulnerability (CWE-918) where an authenticated user can create a link post via POST /api/v3/post. When the post is in a public community, the backend asynchronously sends a Webmention to the URL provided. Although the URL is checked for syntax and scheme, the code does not prevent requests to internal network addresses such as loopback or private IPs. This allows an attacker to induce the server to make HTTP requests to internal services. The vulnerability is patched in version 0.19.18.
Potential Impact
An authenticated low-privileged user can exploit this SSRF vulnerability to make the Lemmy server perform HTTP requests to internal or private network resources. This could potentially expose internal services or data accessible only from the server's network. The CVSS score of 6.3 (medium severity) reflects limited confidentiality, integrity, and availability impacts. There are no known exploits in the wild at this time.
Mitigation Recommendations
Upgrade Lemmy to version 0.19.18 or later, where this SSRF vulnerability is patched. Since this is a self-hosted product, administrators must apply the update to remediate the issue. Patch status is confirmed by the vendor's versioning information. No additional mitigations are specified.
CVE-2026-42180: CWE-918: Server-Side Request Forgery (SSRF) in LemmyNet lemmy
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-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
LemmyNet's lemmy software before version 0.19.18 contains an SSRF vulnerability (CWE-918) where an authenticated user can create a link post via POST /api/v3/post. When the post is in a public community, the backend asynchronously sends a Webmention to the URL provided. Although the URL is checked for syntax and scheme, the code does not prevent requests to internal network addresses such as loopback or private IPs. This allows an attacker to induce the server to make HTTP requests to internal services. The vulnerability is patched in version 0.19.18.
Potential Impact
An authenticated low-privileged user can exploit this SSRF vulnerability to make the Lemmy server perform HTTP requests to internal or private network resources. This could potentially expose internal services or data accessible only from the server's network. The CVSS score of 6.3 (medium severity) reflects limited confidentiality, integrity, and availability impacts. There are no known exploits in the wild at this time.
Mitigation Recommendations
Upgrade Lemmy to version 0.19.18 or later, where this SSRF vulnerability is patched. Since this is a self-hosted product, administrators must apply the update to remediate the issue. Patch status is confirmed by the vendor's versioning information. No additional mitigations are specified.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-04-25T01:53:21.582Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69fe4242cbff5d8610241d6d
Added to database: 5/8/2026, 8:06:26 PM
Last enriched: 5/8/2026, 8:22:11 PM
Last updated: 5/9/2026, 1:59:22 AM
Views: 4
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.