Vulnerability · Published Jan 19, 2026 · Assigned by GitHub_M

CVE-2026-23845Mailpit Vulnerable to Server-Side Request Forgery (SSRF) via HTML Check API

Medium 5.8

In plain English

A medium-severity server-side request forgery in mailpit from axllent. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.8Medium

Exploit odds (30 days)0.4%top 62.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/axllent/mailpit	1.28.3	GHSA-6jxm-fv7w-rw5j
Go	github.com/axllent/mailpit	1.28.3	GO-2026-4345

Affected products (as reported)

Vendor	Product	Versions
axllent	mailpit	< 1.28.3

Weakness: CWE-918 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N

References

https://github.com/axllent/mailpit/security/advisories/GHSA-6jxm-fv7w-rw5j x_refsource_CONFIRM
https://github.com/axllent/mailpit/commit/1679a0aba592ebc8487a996d37fea8318c984dfe x_refsource_MISC
https://github.com/axllent/mailpit/releases/tag/v1.28.3 x_refsource_MISC