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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

Quick assessment

Affected
axllent mailpit
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

axllent mailpit是axllent个人开发者开源的一款邮件测试与调试工具。 Ralph Slooten Mailpit 1.28.3版本至1.30.0之前版本存在服务端请求伪造漏洞，该漏洞源于internal/htmlcheck/css.go::newSafeHTTPClient函数构建的http.Client未添加IP白名单，且允许重定向跳转至任意URL，导致存在服务端请求伪造漏洞，可能允许未经身份验证的攻击者通过发送HTML邮件并触发/api/v1/message/{id}/html-ch

CVSS 5.8 · Medium EPSS 0.32% · P23

Affected Version Matrix 1

VendorProduct Version RangeStatus
axllent mailpit >= 1.28.3, < 1.30.0 affected
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I. Basic Information for CVE-2026-45709

Vulnerability Information
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Vulnerability Title
Mailpit has an incomplete fix for GHSA-6jxm: HTML check still permits SSRF to private/loopback/IMDS via missing IP-filter dialer
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5
Vulnerability Title
Ralph Slooten Mailpit 服务端请求伪造漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
axllent mailpit是axllent个人开发者开源的一款邮件测试与调试工具。 Ralph Slooten Mailpit 1.28.3版本至1.30.0之前版本存在服务端请求伪造漏洞，该漏洞源于internal/htmlcheck/css.go::newSafeHTTPClient函数构建的http.Client未添加IP白名单，且允许重定向跳转至任意URL，导致存在服务端请求伪造漏洞，可能允许未经身份验证的攻击者通过发送HTML邮件并触发/api/v1/message/{id}/html-ch
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
axllent mailpit >= 1.28.3, < 1.30.0 -

II. Public POCs for CVE-2026-45709

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III. Intelligence Information for CVE-2026-45709

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Vendor Advisories for CVE-2026-45709 (1)

Vendor Pages for CVE-2026-45709 (1)

Same Patch Batch · axllent · 2026-07-20 · 5 CVEs total

CVE-2026-45713 7.5 HIGH Mailpit: Unauthenticated remote memory-exhaustion DoS via unlimited SMTP DATA and /api/v1/
CVE-2026-45712 5.9 MEDIUM Mailpit: Concurrent map read & write in proxy CSS rewriter - remote unauth crash (fatal er
CVE-2026-45711 5.9 MEDIUM Mailpit: Path traversal & arbitrary file write in mailpit dump --http via attacker-control
CVE-2026-48824 5.3 MEDIUM Mailpit: Sibling-endpoint memory-exhaustion DoS via unbounded JSON body on /api/v1/message

IV. Related Vulnerabilities

Same product: mailpit
Same vendor: axllent
Same weakness: CWE-918

V. Comments for CVE-2026-45709

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