CVE-2026-45709 Details
Description
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.
A server-side request forgery (SSRF) vulnerability has been identified in Mailpit, an email testing tool for developers. This issue arises in versions 1.28.3 and later, prior to 1.30.0, specifically within the HTML Check API. The vulnerability allows the server to make HTTP requests to internal loopback, private, link-local, and reserved/multicast IP ranges, bypassing security measures that are supposed to block such access. The flaw can be exploited by sending an HTML email that includes a link to an external CSS file controlled by the attacker. When the email is processed, Mailpit follows the link, potentially redirecting the request to a private network resource without detection.
Users are advised to upgrade to Mailpit version 1.30.0, which includes a proper fix for this vulnerability by adding the necessary IP filtering to the HTML Check API.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Jul 20, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/axllent/mailpit/releases/tag/v1.30.0 | [email protected] | Release Notes |
| https://github.com/axllent/mailpit/security/advisories/GHSA-j3fj-qppj-fmmc | [email protected] | ExploitVendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-918 | Server-Side Request Forgery (SSRF) | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| axllent mailpit | >= 1.28.3, < 1.30.0 |
CPE
Remediation
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Change History
3 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 28, 2026 | Initial Analysis | [email protected] |
| Jul 20, 2026 | CVE Modified | CISA-ADP |
| Jul 20, 2026 | New CVE Received | [email protected] |