SSRF (Server-Side Request Forgery) in github.com/axllent/mailpit (CVE-2026-45709)
Summary
SSRF in github.com/axllent/mailpit (CVE-2026-45709). Risk of unauthorized operations or information disclosure. Exploitable via GET /api/v1/message/{id}/html-check. Mitigation: upgrade to 1.30.0 or later.
Original description
The description as published by the source.
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 co…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-45709 has been found in github.com/axllent/mailpit.
Attackers can target a specific entry point like GET /api/v1/message/{id}/html-check over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.8/10.
What to do: upgrade github.com/axllent/mailpit to 1.30.0 or later.
If unsure, ask your IT team or search "github.com/axllent/mailpit CVE-2026-45709" on the vendor's site.
CVE-2026-45709 (github.com/axllent/mailpit) — CWE-918 / CVSS v3 5.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: GET /api/v1/message/{id}/html-check / GET /admin/restart / GET /vacuum / GET /flush
Patched: 1.30.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
SSRF (CWE-918) exists in github.com/axllent/mailpit. Attackers reach the vulnerable code path via GET /api/v1/message/{id}/html-check without authentication.
Check the vendor advisory for the affected versions of github.com/axllent/mailpit. Attack surface: GET /api/v1/message/{id}/html-check / GET /admin/restart / GET /vacuum / GET /flush.
Severity: Medium (CVSS 5.8/10). Risk of unauthorized operations or information disclosure.
Update to 1.30.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual GET /api/v1/message/{id}/html-check requests with malformed payloads or SQL meta-characters. Run grep -r 'github.com/axllent/mailpit' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'github.com/axllent/mailpit' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/axllent/mailpitを grep し、稼働しているサービス・バージョンを把握する。 -
2Hunt for indicators of compromise detect
grep 'GET /api/v1/message/{id}/html-check' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
GET /api/v1/message/{id}/html-checkへの異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Apply patch patch
Upgrade github.com/axllent/mailpit to 1.30.0ステージング環境で 1.30.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスと、Step 2 で見つけた異常検知の続報チェックを含めること。
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4Post-deployment verification verify
Replay attack against GET /api/v1/message/{id}/html-check on staging to confirm patch closes the vectorパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番では Step 2 と同じログクエリでアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- web github.com
- web github.com