# CVE-2026-45709: Mailpit has an incomplete fix for GHSA-6jxm: HTML check still permits SSRF to private/loopback/IMDS via missing IP-filter dialer

> Unauthenticated attackers can trigger Server-Side Request Forgery in Mailpit to access internal network resources via the HTML check API.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Jul 2026
- **Updated:** 20 Jul 2026
- **Also known as:** GHSA-j3fj-qppj-fmmc, GO-2026-5446

## What is CVE-2026-45709?

CVE-2026-45709 is a medium-severity server-side request forgery vulnerability in axllent mailpit, published on 20 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-45709?

3 open source packages ship an affected version, including github.com/axllent/mailpit. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/axllent/mailpit` | Go | From 1.28.3 | 1.30.0 |
| `github.com/axllent/mailpit` | Go | From 1.28.3 | 1.30.0 |
| `github.com/axllent/mailpit` | Go | From 1.28.3 | 1.30.0 |

Products: Axllent Mailpit.

## How do I fix CVE-2026-45709?

Upgrade github.com/axllent/mailpit to 1.30.0 or later.

## Is CVE-2026-45709 being exploited?

There is no known exploitation of CVE-2026-45709 in the wild and no public exploit code.

## Other vulnerabilities in axllent mailpit

- [CVE-2026-45713](https://insights.sbomify.com/CVE-2026-45713/): Mailpit: Unauthenticated remote memory-exhaustion DoS via unlimited SMTP DATA and /api/v1/send body sizes (high 7.5)
- [CVE-2026-22689](https://insights.sbomify.com/CVE-2026-22689/): Mailpit is vulnerable to Cross-Site WebSocket Hijacking (CSWSH) allowing unauthenticated access to emails (medium 6.5)
- [CVE-2026-45711](https://insights.sbomify.com/CVE-2026-45711/): Mailpit: Path traversal & arbitrary file write in mailpit dump --http via attacker-controlled message IDs (medium 5.9)
- [CVE-2026-45712](https://insights.sbomify.com/CVE-2026-45712/): Mailpit: Concurrent map read & write in proxy CSS rewriter - remote unauth crash (fatal error: concurrent map read and map write) (medium 5.9)
- [CVE-2026-27808](https://insights.sbomify.com/CVE-2026-27808/): Mailpit is Vulnerable to Server-Side Request Forgery (SSRF) via Link Check API (medium 5.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45709 and fix it if it is affected.

What it is: CVE-2026-45709 is a medium-severity server-side request forgery vulnerability in axllent mailpit, published on 20 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-45709 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/axllent/mailpit (Go): affected from 1.28.3; fixed in 1.30.0
- github.com/axllent/mailpit (Go): affected from 1.28.3; fixed in 1.30.0
- github.com/axllent/mailpit (Go): affected from 1.28.3; fixed in 1.30.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-45709/ (Markdown: https://insights.sbomify.com/CVE-2026-45709/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45709
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45709
- OSV: https://osv.dev/vulnerability/CVE-2026-45709

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45709/
Summaries are generated and may contain mistakes; the official description above is the record.