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 post with a link that causes the server to asynchronously send a Webmention HTTP request to the target URL. The URL validation only checks syntax and scheme but fails to restrict requests to internal network addresses such as loopback or private IPs. This flaw allows low-privileged users to induce server-side HTTP requests to internal services, potentially exposing internal resources or causing other impacts. The vulnerability is patched in version 0.19.18.
Potential Impact
The vulnerability allows an authenticated low-privileged user to cause the Lemmy server to make HTTP requests to internal or otherwise restricted network addresses. This could lead to information disclosure or interaction with internal services that are not normally accessible externally. The CVSS score of 6.3 reflects a medium severity with potential confidentiality, integrity, and availability impacts. There are no known exploits in the wild at this time.
Mitigation Recommendations
This vulnerability is fixed in Lemmy version 0.19.18. Users should upgrade to version 0.19.18 or later to remediate this issue. No other vendor advisory or patch information is provided, so patch status beyond this version upgrade is not confirmed. Until upgraded, restrict access to trusted users and monitor for suspicious activity related to Webmention requests if possible.
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.
CVSS v3.1
Score 6.3medium
Affected software
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Weaknesses
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 post with a link that causes the server to asynchronously send a Webmention HTTP request to the target URL. The URL validation only checks syntax and scheme but fails to restrict requests to internal network addresses such as loopback or private IPs. This flaw allows low-privileged users to induce server-side HTTP requests to internal services, potentially exposing internal resources or causing other impacts. The vulnerability is patched in version 0.19.18.
Potential Impact
The vulnerability allows an authenticated low-privileged user to cause the Lemmy server to make HTTP requests to internal or otherwise restricted network addresses. This could lead to information disclosure or interaction with internal services that are not normally accessible externally. The CVSS score of 6.3 reflects a medium severity with potential confidentiality, integrity, and availability impacts. There are no known exploits in the wild at this time.
Mitigation Recommendations
This vulnerability is fixed in Lemmy version 0.19.18. Users should upgrade to version 0.19.18 or later to remediate this issue. No other vendor advisory or patch information is provided, so patch status beyond this version upgrade is not confirmed. Until upgraded, restrict access to trusted users and monitor for suspicious activity related to Webmention requests if possible.
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: 05/08/2026, 20:06:26 UTC
Last enriched: 05/16/2026, 09:41:29 UTC
Last updated: 07/31/2026, 19:22:58 UTC
Views: 89
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