CVE-2026-23845: axllent mailpit Server-Side Request Forgery (SSRF)

Vulnerability summary

CVE-2026-23845 is a high (CVSS 7.5) Server-Side Request Forgery (SSRF) vulnerability in axllent mailpit. EPSS estimates a 0.43% chance of exploitation in the next 30 days, higher than 35.9% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 19-01-2026
   PublishedVulnerability first disclosed.
2. 20-01-2026
   Last modifiedVulnerability information updated.

Description

Mailpit is an email testing tool and API for developers. Versions prior to 1.28.3 are vulnerable to Server-Side Request Forgery (SSRF) via HTML Check CSS Download. The HTML Check feature (`/api/v1/message/{ID}/html-check`) is designed to analyze HTML emails for compatibility. During this process, the `inlineRemoteCSS()` function automatically downloads CSS files from external `<link rel="stylesheet" href="...">` tags to inline them for testing. Version 1.28.3 fixes the issue.

• CWE-918Server-Side Request Forgery (SSRF)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.