CVE-2026-45709

What it is

Mailpit is an email testing tool and API for developers. 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). Prior to version 1.30.0, `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, private, link-local, and any other reserved/multicast range, provided the target replies with `HTTP/200` and a content-type beginning with `text/css`. With redirect-following (`CheckRedirect` allows redirects to any `isValidURL` URL with no IP filter), an attacker-controlled public site can redirect mailpit's request into the private network without ever appearing in the email's HTML. In the default mailpit deploy (no UI auth, no SMTP auth, port 1025/8025 exposed), this is an unauthenticated, network-reachable SSRF triggered by sending an HTML email and then issuing one HTTP `GET` to `/api/v1/message/{id}/html-check`. Version 1.30.0 contains an updated fix.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-07-20 16:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-24 20:10 UTC Last updatedMost recent change to the record

Details

Published

2026-07-20 16:17 UTC

Last modified

2026-10-24 20:10 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-918 · Server-side request forgery

Record status

Analyzed

Affected

• Axllent Mailpit < 1.30.0

Attack profile CVSS 3.1 · 5.8

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

Low

Availability

None