CVE-2026-22689

Ein entfernter, anonymer Angreifer kann eine Schwachstelle in MailPit ausnutzen, um Informationen offenzulegen.

**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 real-time. **Vulnerable Code** The vulnerability exists in server/websockets/client.go where the CheckOrigin function is explicitly set to return true for all requests, bypassing standard Same-Origin Policy (SOP) protections provided by the gorilla/websocket library. https://github.com/axllent/mailpit/blob/877a9159ceeaf380d5bb0e1d84017b24d2e7b361/server/websockets/client.go#L34-L39 **Impact** This vulnerability impacts the Confidentiality of the data stored in or processed by Mailpit. Although Mailpit is often used as a local development tool, this vulnerability allows remote exploitation via a web browser. - **Scenario**: A developer has Mailpit running at localhost:8025. - **Trigger**: The developer visits a malicious website (or a compromised legitimate site) in the same browser. - **Exploitation**: The malicious site's JavaScript initiates a WebSocket connection to ws://localhost:8025/api/events. Since the origin check is disabled, the browser allows this cross-origin connection. - **Data Leak**: The attacker receives all broadcasted events, including full email details (subjects, sender/receiver info) and server metrics. **Attack Impact** - Real-time notification of new emails - Email metadata (sender, subject, recipients) - Mailbox statistics - All WebSocket broadcast data **Recommended Fix** The `CheckOrigin` function should be removed to allow gorilla/websocket to enforce its default safe behavior (checking that the Origin matches the Host). Alternatively, strict validation logic should be implemented. **Proposed Change (Remove unsafe check):** ```go var upgrader = websocket.Upgrader{ ReadBufferSize: 1024, WriteBufferSize: 1024, // CheckOrigin: func(r *http.Request) bool { return true }, // REMOVED EnableCompression: true, } ``` **Proof of Concept (PoC)**: To reproduce this vulnerability: - Start Mailpit (default settings). - Save the following HTML code as poc.html and serve it from a different origin (e.g., using python http.server on port 8000 or opening it directly as a file). - Open the [poc_websocket_hijack.html](https://github.com/user-attachments/files/24522726/poc_websocket_hijack.html) file in your browser. - Send a test email to Mailpit or perform any action in the Mailpit UI. - Observe that the "malicious" page successfully receives the event data.

Mailpit is vulnerable to Cross-Site WebSocket Hijacking (CSWSH) allowing unauthenticated access to emails in github.com/axllent/mailpit. NOTE: The source advisory for this report contains additional versions that could not be automatically mapped to standard Go module versions. (If this is causing false-positive reports from vulnerability scanners, please suggest an edit to the report.) The additional affected modules and versions are: github.com/axllent/mailpit before v0.0.0-20260110031614.