# CVE-2026-45709: Axllent Mailpit SSRF in HTML Check API

Source: https://junglewise.ai/threats/cve-2026-45709-axllent-mailpit-ssrf-in-html-check-api  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-20. Updated: 2026-07-20  
License: CC BY 4.0 with a link back

CVE-2026-45709 · Severity: medium · CVSS 5.8 · Published 2026-07-20

Mailpit, a tool used by developers to test email functionality, contains a security flaw in its HTML checking feature. An attacker can send a specially crafted email that forces the Mailpit server to make unauthorized requests to internal network services, such as private databases or administrative interfaces. This could allow an attacker to trigger actions on internal systems that are not supposed to be accessible from the outside, potentially disrupting operations or modifying internal configurations.

Technologies: [Axllent Mailpit](https://junglewise.ai/threats/technologies/mailpit), [github.com/axllent/mailpit (Go)](https://junglewise.ai/threats/technologies/github-com-axllent-mailpit). Vendors: [Axllent](https://junglewise.ai/threats/vendors/axllent), [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-45709 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-45709 being exploited in the wild.

**How severe is CVE-2026-45709?** Medium severity, with a CVSS score of 5.8, published 20 July 2026.

**Which products and versions are affected?** Axllent Mailpit >= 1.28.3, < 1.30.0; github.com/axllent/mailpit (Go) >= 1.28.3, < 1.30.0, SEMVER:introduced=1.28.3,fixed=1.30.0.

**Is there a fix for CVE-2026-45709?** Yes. github.com/axllent/mailpit (Go): upgrade to 1.30.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-45709 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-45709?** Check whether you run Axllent Mailpit or github.com/axllent/mailpit (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/axllent/mailpit (Go): upgrade to 1.30.0 or later

  ```sh
  go get github.com/axllent/mailpit@v1.30.0
  ```


## Technical details

This vulnerability is an incomplete fix for CVE-2026-23845. While previous hardening added size limits and content-type checks to the CSS downloader in 'internal/htmlcheck/css.go', it failed to implement an IP-filtering dialer. The 'newSafeHTTPClient' function lacks IP allowlisting in its 'Transport.DialContext', allowing the server to dial loopback (127.0.0.1), private (RFC1918), and link-local (IMDS) addresses. An attacker can exploit this by sending an HTML email with a stylesheet link pointing to an attacker-controlled server, which then issues a 302 redirect to an internal target. The SSRF is triggered via an unauthenticated GET request to the '/api/v1/message/{id}/html-check' endpoint. This allows for state-changing internal GET requests against local services. The issue is resolved in version 1.30.0.

## Affected products

- axllent Mailpit >= 1.28.3, < 1.30.0

## Identifiers

- CVE-2026-45709
- GHSA-j3fj-qppj-fmmc
- GO-2026-5446

## Timeline

- 2026-05-14: patched: Version 1.30.0 released with fix
- 2026-07-20: disclosed: CVE-2026-45709 published

## References

- [https://github.com/axllent/mailpit/releases/tag/v1.30.0](https://github.com/axllent/mailpit/releases/tag/v1.30.0)
- [https://github.com/axllent/mailpit/security/advisories/GHSA-j3fj-qppj-fmmc](https://github.com/axllent/mailpit/security/advisories/GHSA-j3fj-qppj-fmmc)

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