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.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-45709)

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by multiple vulnerabilities as referenced in the 6e701ad2-4f61-11f1-af6d-10ffe07f9334 advisory.

    Mailpit author reports:
    Set a default 50MB per message limit to prevent DoS via              unlimited SMTP DATA and /api/v1/send body sizes              (GHSA-fpxj-m5q8-fphw)     Include CGNAT (Carrier-Grade NAT) in internal IP checks              (GHSA-j3fj-qppj-fmmc)     Block internal IP access by default in HTML check              (GHSA-j3fj-qppj-fmmc)     Fix for path traversal & arbitrary file write in              mailpit dump --http <instance> via attacker-controlled              message IDs (GHSA-qx5x-85p8-vg4j)     Fix concurrent map read & write in proxy CSS rewriter              (GHSA-w4vj-r5pg-3722)

Tenable has extracted the preceding description block directly from the FreeBSD security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Type	Severity
442155	SCA: security update for github.com/axllent/mailpit (GHSA-j3fj-qppj-fmmc)	Tenable Cloud Security	SCA Checks	Local	medium
442155	SCA: security update for github.com/axllent/mailpit (GHSA-j3fj-qppj-fmmc)	Tenable Self-Hosted Container Security	SCA Checks	Local	medium
314913	FreeBSD : mail/mailpit -- multiple vulnerabilities (6e701ad2-4f61-11f1-af6d-10ffe07f9334)	Nessus	FreeBSD Local Security Checks	Local	high

Detections

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CVE-2026-45709

medium

Tenable Plugins

medium

medium

high