The remediation shipped in mailpit v1.29.2 for GHSA-mpf7-p9x7-96r3 (CVE-2026-27808) is incomplete. The tools.IsInternalIP deny-list relies on Go's stdlib classification helpers (IsLoopback, IsPrivate, IsLinkLocalUnicast, IsLinkLocalMulticast, IsUnspecified, IsMulticast) plus an inline CGNAT range, but those helpers do not match two classes of IPv6 address that should be blocked for SSRF purposes: IPv6 forms that embed an IPv4 destination via documented translation mechanisms — 6to4, NAT64, IPv4-compatible IPv6, ISATAP, or (in older Go …
The Mailpit SMTP server has a Server.MaxSize int field that controls the maximum allowed DATA payload size, but the field is never assigned anywhere outside test code, leaving it at Go's zero value (0 ⇒ "no limit"). The same applies to the HTTP /api/v1/send endpoint, whose request body is decoded with json.NewDecoder(r.Body) and no http.MaxBytesReader. Because Mailpit's default listeners bind [::]:1025 (SMTP) and [::]:8025 (HTTP), with no authentication required on …
The mailpit dump –http sub-command downloads every message from a remote Mailpit instance and writes each one as .eml inside the user-supplied output directory. The message ID field is taken verbatim from the JSON response of the remote server and concatenated into the output path with path.Join, which silently normalizes .. segments. A malicious HTTP server impersonating Mailpit can therefore make mailpit dump write attacker-controlled bytes to any path the …
The screenshot/print proxy (/proxy?data=…) maintains a package-level assets map[string]MessageAssets cache, but reads the map without holding assetsMutex while a long-running cleanup goroutine and (re-entrant) CSS-rewriting code path concurrently write to it under the lock. When the unsynchronized read coincides with a synchronized write, Go's runtime raises fatal error: concurrent map read and map write — a runtime.throw that is not recoverable by http.Server's handler-panic recover. The whole Mailpit process exits, …
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). At HEAD 8bc966e61834a24c48b4465da418f75e73be0afd (2026-05-06), internal/htmlcheck/css.go::newSafeHTTPClient is mis-named …
The Link Check API (/api/v1/message/{ID}/link-check) is vulnerable to Server-Side Request Forgery (SSRF). The server performs HTTP HEAD requests to every URL found in an email without validating target hosts or filtering private/internal IP addresses. The response returns status codes and status text per link, making this a non-blind SSRF. In the default configuration (no authentication on SMTP or API), this is fully exploitable remotely with zero user interaction. This is …
Server-Side Request Forgery (SSRF) via HTML Check CSS Download The HTML Check feature (/api/v1/message/{ID}/html-check) is designed to analyze HTML emails for compatibility. During this process, the inlineRemoteCSS() function automatically downloads CSS files from external <link rel="stylesheet" href="…"> tags to inline them for testing. Affected Components Primary File: internal/htmlcheck/css.go (lines 132-207) API Endpoint: /api/v1/message/{ID}/html-check Handler: server/apiv1/other.go (lines 38-75) Vulnerable Functions: inlineRemoteCSS() - line 132 downloadToBytes() - line 193 isURL() - line …
Mailpit's SMTP server is vulnerable to Header Injection due to an insufficient Regular Expression used to validate RCPT TO and MAIL FROM addresses. An attacker can inject arbitrary SMTP headers (or corrupt existing ones) by including carriage return characters (\r) in the email address. This header injection occurs because the regex intended to filter control characters fails to exclude \r and \n when used inside a character class.
Summary The Mailpit WebSocket server is configured to accept connections from any origin. This lack of Origin header validation introduces a Cross-Site WebSocket Hijacking (CSWSH) vulnerability. An attacker can host a malicious website that, when visited by a developer running Mailpit locally, establishes a WebSocket connection to the victim's Mailpit instance (default ws://localhost:8025). This allows the attacker to intercept sensitive data such as email contents, headers, and server statistics in …
A Server-Side Request Forgery (SSRF) vulnerability exists in Mailpit's /proxy endpoint that allows attackers to make requests to internal network resources.