Eclipse Jetty URI parsing of invalid authority

Summary

Eclipse Jetty is a lightweight, highly scalable, Java-based web server and Servlet engine . It includes a utility class, HttpURI, for URI/URL parsing.

The HttpURI class does insufficient validation on the authority segment of a URI. However the behaviour of HttpURI differs from the common browsers in how it handles a URI that would be considered invalid if fully validated against the RRC. Specifically HttpURI and the browser may differ on the value of the host extracted from an invalid URI and thus a combination of Jetty and a vulnerable browser may be vulnerable to a open redirect attack or to a SSRF attack if the URI is used after passing validation checks.

Details

Affected components

The vulnerable component is the HttpURI class when used as a utility class in an application. The Jetty usage of the class is not vulnerable.

Attack overview

The HttpURI class does not well validate the authority section of a URI. When presented with an illegal authority that may contain user info (eg username:password#@hostname:port), then the parsing of the URI is not failed. Moreover, the interpretation of what part of the authority is the host name differs from a common browser in that they also do not fail, but they select a different host name from the illegal URI.

Attack scenario

A typical attack scenario is illustrated in the diagram below. The Validator checks whether the attacker-supplied URL is on the blocklist. If not, the URI is passed to the Requester for redirection. The Requester is responsible for sending requests to the hostname specified by the URI.

This attack occurs when the Validator is the org.eclipse.jetty.http.HttpURI class and the Requester is the Browser (include chrome, firefox and Safari). An attacker can send a malformed URI to the Validator (e.g., http://browser.check%23%40vulndetector.com/ ). After validation, the Validator finds that the hostname is not on the blocklist. However, the Requester can still send requests to the domain with the hostname vulndetector.com.

PoC

payloads:

http://browser.check &@vulndetector.com/
http://browser.check #@vulndetector.com/
http://browser.check?@vulndetector.com/
http://browser.check#@vulndetector.com/
http://vulndetector.com\\/

The problem of 302 redirect parsing in HTML tag scenarios. Below is a poc example. After clicking the button, the browser will open "browser.check", and jetty will parse this URL as "vulndetector.com".

<a href="http://browser.check#@vulndetector.com/"></a>

A comparison of the parsing differences between Jetty and chrome is shown in the table below (note that neither should accept the URI as valid).

The problem of 302 redirect parsing in HTTP 302 Location

It is noteworthy that Spring Web also faced similar security vulnerabilities, being affected by the aforementioned four types of payloads. These issues have since been resolved and have been assigned three CVE numbers [3-5].

Impact

The impact of this vulnerability is limited to developers that use the Jetty HttpURI directly. Example: your project implemented a blocklist to block on some hosts based on HttpURI's handling of authority section. The vulnerability will help attackers bypass the protections that developers have set up for hosts. The vulnerability will lead to SSRF[1] and URL Redirection[2] vulnerabilities in several cases.

Mitigation

The attacks outlined above rely on decoded user data being passed to the HttpURI class. Application should not pass decoded user data as an encoded URI to any URI class/method, including HttpURI. Such applications are likely to be vulnerable in other ways. The immediate solution is to upgrade to a version of the class that will fully validate the characters of the URI authority. Ultimately, Jetty will deprecate and remove support for user info in the authority per RFC9110 Section 4.2.4.

Note that the Chrome (and other browsers) parse the invalid user info section improperly as well (due to flawed WhatWG URL parsing rules that do not apply outside of a Web Browser).

Reference

[1] https://cwe.mitre.org/data/definitions/918.html [2] https://cwe.mitre.org/data/definitions/601.html