Hono Streaming Helper SSE Control Field Injection Vulnerability

A vulnerability in the Hono web application framework, prior to version 4.12.4, allows for injection of additional Server-Sent Events (SSE) fields within the same event frame. This issue arises because the framework's Streaming Helper did not validate the event, id, and retry fields for carriage return or newline characters. Since the SSE protocol uses line breaks as field delimiters, untrusted input could be exploited to manipulate the event stream. The vulnerability has been patched in version 4.12.4.

Impact

Exploitation of this vulnerability could lead to unintended manipulation of SSE event frames, allowing injection of additional fields or alteration of event stream handling. This could be particularly problematic for applications that render SSE data in an unsafe manner, potentially exposing them to client-side script injection.

Reproduction

The vulnerability can be reproduced by using the streamSSE() function in the Hono Streaming Helper with untrusted input that includes carriage return or newline characters in the event, id, or retry fields. This can be done by writing an SSE event that contains these characters, which will be processed by the Streaming Helper without proper validation, allowing the injection of additional SSE fields into the event stream.

Remediation

Users should update to Hono version 4.12.4 or later, where this vulnerability has been fixed.