CVE-2026-42180 — MEDIUM (6.3)

Vulnerability 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 Score

6.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

LOW

Integrity

LOW

Availability

LOW

Related Weaknesses (CWE)

CWE-918

References

FAQ

What is CVE-2026-42180?

CVE-2026-42180 is a vulnerability with a CVSS score of 6.3 (MEDIUM). 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 crea...

How severe is CVE-2026-42180?

CVE-2026-42180 has been rated MEDIUM with a CVSS base score of 6.3/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-42180?

Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.