Package Instance

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).

| Invalid URI                                       | Jetty            | Chrome        |
| ---------------------------------------------- | ---------------- | ------------- |
| http://browser.check &@vulndetector.com/ | vulndetector.com | browser.check |
| http://browser.check #@vulndetector.com/ | vulndetector.com | browser.check |
| http://browser.check?@vulndetector.com/    | vulndetector.com | browser.check |
| http://browser.check#@vulndetector.com/    | vulndetector.com | browser.check |

The problem of 302 redirect parsing in HTTP 302 Location

| Input                    | Jetty          | Chrome        |
| ------------------------ | -------------- | ------------- |
| http://browser.check%5c/ | browser.check\ | browser.check |

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](https://datatracker.ietf.org/doc/html/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

Information Exposure
In Eclipse Jetty, the server running on any OS and Jetty version combination will reveal the configured fully qualified directory base resource location on the output of the error for not finding a Context that matches the requested path. The default server behavior on jetty-distribution and jetty-home will include at the end of the Handler tree a `DefaultHandler`, which is responsible for reporting this error, it presents the various configured contexts as HTML for users to click through to. This produced HTML includes output that contains the configured fully qualified directory base resource location for each context.

Local Temp Directory Hijacking Vulnerability
### Impact
On Unix like systems, the system's temporary directory is shared between all users on that system.  A collocated user can observe the process of creating a temporary sub directory in the shared temporary directory and race to complete the creation of the temporary subdirectory.  If the attacker wins the race then they will have read and write permission to the subdirectory used to unpack web applications, including their WEB-INF/lib jar files and JSP files.  If any code is ever executed out of this temporary directory, this can lead to a local privilege escalation vulnerability.

Additionally, any user code uses of [WebAppContext::getTempDirectory](https://www.eclipse.org/jetty/javadoc/9.4.31.v20200723/org/eclipse/jetty/webapp/WebAppContext.html#getTempDirectory()) would similarly be vulnerable.

Additionally, any user application code using the `ServletContext` attribute for the tempdir will also be impacted.
See: https://javaee.github.io/javaee-spec/javadocs/javax/servlet/ServletContext.html#TEMPDIR

For example:
```java
import java.io.File;
import java.io.IOException;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ExampleServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        File tempDir = (File)getServletContext().getAttribute(ServletContext.TEMPDIR); // Potentially compromised
        // do something with that temp dir
    }
}
```

Example: The JSP library itself will use the container temp directory for compiling the JSP source into Java classes before executing them.

### CVSSv3.1 Evaluation

This vulnerability has been calculated to have a [CVSSv3.1 score of 7.8/10 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)](https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H&version=3.1)

### Patches
Fixes were applied to the 9.4.x branch with:
- https://github.com/eclipse/jetty.project/commit/53e0e0e9b25a6309bf24ee3b10984f4145701edb
- https://github.com/eclipse/jetty.project/commit/9ad6beb80543b392c91653f6bfce233fc75b9d5f

These will be included in releases: 9.4.33, 10.0.0.beta3, 11.0.0.beta3

### Workarounds

A work around is to set a temporary directory, either for the server or the context, to a directory outside of the shared temporary file system.
For recent releases, a temporary directory can be created simple by creating a directory called `work` in the ${jetty.base} directory (the parent directory of the `webapps` directory).
Alternately the java temporary directory can be set with the System Property `java.io.tmpdir`.    A more detailed description of how jetty selects a temporary directory is below.

The Jetty search order for finding a temporary directory is as follows:

1. If the [`WebAppContext` has a temp directory specified](https://www.eclipse.org/jetty/javadoc/current/org/eclipse/jetty/webapp/WebAppContext.html#setTempDirectory(java.io.File)), use it.
2. If the `ServletContext` has the `javax.servlet.context.tempdir` attribute set, and if directory exists, use it.
3. If a `${jetty.base}/work` directory exists, use it (since Jetty 9.1)
4. If a `ServletContext` has the `org.eclipse.jetty.webapp.basetempdir` attribute set, and if the directory exists, use it.
5. Use `System.getProperty("java.io.tmpdir")` and use it.

Jetty will end traversal at the first successful step.
To mitigate this vulnerability the directory must be set to one that is not writable by an attacker.  To avoid information leakage, the directory should also not be readable by an attacker.

#### Setting a Jetty server temporary directory.

Choices 3 and 5 apply to the server level, and will impact all deployed webapps on the server.

For choice 3  just create that work directory underneath your `${jetty.base}` and restart Jetty.

For choice 5, just specify your own `java.io.tmpdir` when you start the JVM for Jetty.

``` shell
[jetty-distribution]$ java -Djava.io.tmpdir=/var/web/work -jar start.jar
```

#### Setting a Context specific temporary directory.

The rest of the choices require you to configure the context for that deployed webapp (seen as `${jetty.base}/webapps/<context>.xml`)

Example (excluding the DTD which is version specific):

``` xml
<Configure class="org.eclipse.jetty.webapp.WebAppContext">
  <Set name="contextPath"><Property name="foo"/></Set>
  <Set name="war">/var/web/webapps/foo.war</Set>
  <Set name="tempDirectory">/var/web/work/foo</Set>
</Configure>
```

### References
 
 - https://github.com/eclipse/jetty.project/issues/5451
 - [CWE-378: Creation of Temporary File With Insecure Permissions](https://cwe.mitre.org/data/definitions/378.html)
 - [CWE-379: Creation of Temporary File in Directory with Insecure Permissions](https://cwe.mitre.org/data/definitions/379.html)
 - [CodeQL Query PR To Detect Similar Vulnerabilities](https://github.com/github/codeql/pull/4473)

### Similar Vulnerabilities

Similar, but not the same.

 - JUnit 4 - https://github.com/junit-team/junit4/security/advisories/GHSA-269g-pwp5-87pp
 - Google Guava - https://github.com/google/guava/issues/4011
 - Apache Ant - https://nvd.nist.gov/vuln/detail/CVE-2020-1945
 - JetBrains Kotlin Compiler - https://nvd.nist.gov/vuln/detail/CVE-2020-15824

### For more information

The original report of this vulnerability is below:

> On Thu, 15 Oct 2020 at 21:14, Jonathan Leitschuh <jonathan.leitschuh@gmail.com> wrote:
> Hi WebTide Security Team,
>
> I'm a security researcher writing some custom CodeQL queries to find Local Temporary Directory Hijacking Vulnerabilities. One of my queries flagged an issue in Jetty.
>
> https://lgtm.com/query/5615014766184643449/
>
> I've recently been looking into security vulnerabilities involving the temporary directory because on unix-like systems, the system temporary directory is shared between all users.
> There exists a race condition between the deletion of the temporary file and the creation of the directory.
>
> ```java
> // ensure file will always be unique by appending random digits
> tmpDir = File.createTempFile(temp, ".dir", parent); // Attacker knows the full path of the file that will be generated
> // delete the file that was created
> tmpDir.delete(); // Attacker sees file is deleted and begins a race to create their own directory before Jetty.
> // and make a directory of the same name
> // SECURITY VULNERABILITY: Race Condition! - Attacker beats Jetty and now owns this directory
> tmpDir.mkdirs();
> ```
>
> https://github.com/eclipse/jetty.project/blob/1b59672b7f668b8a421690154b98b4b2b03f254b/jetty-webapp/src/main/java/org/eclipse/jetty/webapp/WebInfConfiguration.java#L511-L518
>
> In several cases the `parent` parameter will not be the system temporary directory. However, there is one case where it will be, as the last fallback.
>
>
> https://github.com/eclipse/jetty.project/blob/1b59672b7f668b8a421690154b98b4b2b03f254b/jetty-webapp/src/main/java/org/eclipse/jetty/webapp/WebInfConfiguration.java#L467-L468
>
> If any code is ever executed out of this temporary directory, this can lead to a local privilege escalation vulnerability.
>
> Would your team be willing to open a GitHub security advisory to continue the discussion and disclosure there? https://github.com/eclipse/jetty.project/security/advisories
>
> **This vulnerability disclosure follows Google's [90-day vulnerability disclosure policy](https://www.google.com/about/appsecurity/) (I'm not an employee of Google, I just like their policy). Full disclosure will occur either at the end of the 90-day deadline or whenever a patch is made widely available, whichever occurs first.**
>
> Cheers,
> Jonathan Leitschuh