Mailpit has an incomplete fix for GHSA-6jxm: HTML check still permits SSRF to private/loopback/IMDS via missing IP-filter dialer

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

EPSS

• CVE-2026-45709: 0.32% estimated exploitation activity in the next 30 days; percentile 24.54 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The fix for GHSA-6jxm-fv7w-rw5j (CVE-2026-23845, "Server-Side Request Forgery (SSRF) via HTML Check API"), shipped in mailpit v1.28.3, hardened internal/htmlcheck/css.go::downloadCSSToBytes with a 5MB size cap, a text/css content-type check, login-info stripping in isValidURL, and an opt-in --block-remote-css-and-fonts config flag — but did not add the IP-filtering dialer that the same codebase already uses on the two sister SSRF endpoints (the proxy handler and link-check). At HEAD 8bc966e61834a24c48b4465da418f75e73be0afd (2026-05-06), internal/htmlcheck/css.go::newSafeHTTPClient is mis-named — it builds an http.Client whose Transport.DialContext calls net.Dialer.DialContext directly with no IP allowlisting. As a result, the SSRF originally reported by Bao Anh Phan still permits the server to dial: - loopback (127.0.0.0/8, ::1), - private (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, fc00::/7), - link-local incl. cloud IMDS (169.254.0.0/16, especially 169.254.169.254), - CGNAT…

Published by the source

19 May 2026, 15:52 UTC

Last modified by the source

2 Sep 2026, 23:39 UTC

Source last checked

26 Oct 2026, 15:28 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-j3fj-qppj-fmmc

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-45709

Advisory: Mailpit has an incomplete fix for GHSA-6jxm: HTML check still permits SSRF to private/loopback/IMDS via missing IP-filter dialer
IDs: CVE-2026-45709, GHSA-j3fj-qppj-fmmc
Record: https://patchnext.com/advisories/cve-2026-45709 (revision 1, source checked 26 Oct 2026, 15:28 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/axllent/mailpit 1.30.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/axllent/mailpit: affected >= 1.28.3, < 1.30.0; fixed in 1.30.0

## Suggested inspection (read-only)
- Go github.com/axllent/mailpit: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/axllent/mailpit.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-j3fj-qppj-fmmc (GitHub-reviewed advisory GHSA-j3fj-qppj-fmmc lists affected ranges: Go github.com/axllent/mailpit >=1.28.3 <1.30.0)

Commands are suggestions: review each one before running it.