Software Engineering Institute

CWE-20: Improper Input Validation

Resin Pro 4.0.39 and possibly earlier versions perform incorrect Unicode transformations on output to HTTP responses for ISO-8859-1. This allows an attacker to bypass filtering/encoding/validation done prior to the output transformation. An attacker can use specially crafted input characters on pages that by default respond with ISO-8859-1 (or can be forced to use it) to bypass filtering/encoding/validation done prior to the output transformation.

It should be noted that Resin's default encoding (charset) is ISO-8859-1.

A remote unauthenticated attacker may be able to perform XSS, Open Redirect, and other attacks that depend on the logic being enforced prior to the transformation and bypassed due to this vulnerability.

Apply an Update

Resin Pro 4.0.40 has been released to address this vulnerability. If you are unable to upgrade, please consider the following workaround.

Restrict Access

As a general good security practice, only allow connections from trusted hosts and networks. Note that restricting access does not prevent XSS or CSRF attacks since the attack comes as an HTTP request from a legitimate user's host. Restricting access would prevent an attacker from accessing the web interface using stolen credentials from a blocked network location.

Restrict content to always use UTF-8 (or other safe charsets)

Using HttpServletResponse.setContentType() to set the response charset to UTF-8. For example: response.setContentType("text/html;charset=UTF-8");

According to Caucho's base documentation, it is possible to change the system wide encoding to use UTF-8 with a single directive.