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Fencer Intel
medium 5.8

CVE-2026-45709 json

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

published 5mo ago modified 16d ago also EUVD-2026-45966 , GHSA-j3fj-qppj-fmmc , GO-2026-5446

cvss
5.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 24%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/axllent/mailpit 1.30.0
  • axllent mailpit 1.30.0
  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

Is CVE-2026-45709 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
3mo ago

Exploit prediction

0.32% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/axllent/mailpit/security/advisories/GHSA-j3fj-qppj-fmmc referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
GitHub 3.1 5.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
go github.com/axllent/mailpit
>=1.28.3, <1.30.0
1.30.0

Affected products

  • axllent mailpit

Classification

Weakness
  • CWE-918 Server-Side Request Forgery

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.