LemmyNet lemmy up to 0.19.17 HTTP Request /api/v3/post server-side request forgery

CVSS Meta Temp Score
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CTI Interest Score
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6.1$0-$5k0.00

Summaryinfo

A vulnerability was found in LemmyNet lemmy up to 0.19.17 and classified as critical. Affected by this issue is some unknown functionality of the file /api/v3/post of the component HTTP Request Handler. The manipulation results in server-side request forgery. This vulnerability is reported as CVE-2026-42180. The attack can be launched remotely. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in LemmyNet lemmy up to 0.19.17. Affected is an unknown code of the file /api/v3/post of the component HTTP Request Handler. The manipulation with an unknown input leads to a server-side request forgery vulnerability. CWE is classifying the issue as CWE-918. The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-42180 since 04/25/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. There are known technical details, but no exploit is available.

Upgrading to version 0.19.18 eliminates this vulnerability.

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Productinfo

Vendor

Name

Version

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.3
VulDB Meta Temp Score: 6.1

VulDB Base Score: 6.3
VulDB Temp Score: 6.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 6.3
CNA Vector (GitHub_M): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Server-side request forgery
CWE: CWE-918
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: lemmy 0.19.18

Timelineinfo

04/25/2026 CVE reserved
05/08/2026 +13 days Advisory disclosed
05/08/2026 +0 days VulDB entry created
05/08/2026 +0 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-42180 (🔒)
GCVE (CVE): GCVE-0-2026-42180
GCVE (VulDB): GCVE-100-362352

Entryinfo

Created: 05/08/2026 22:21
Changes: 05/08/2026 22:21 (65)
Complete: 🔍
Cache ID: 216::103

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