Vulnerability Note VU#719225
Apache Struts2 ClassLoader allows access to class properties via request parameters
Original Release date: 25 Apr 2014 | Last revised: 28 Apr 2014

Overview
Apache Struts2 2.3.16.1 and earlier contain a vulnerability where the ClassLoader allows access to class properties via request parameters

Description
Apache Struts2 2.3.16.1 and earlier contain a vulnerability where the ClassLoader allows access to class properties via request parameters. This vulnerability was previously attempted to be addressed in S2-020 ClassLoader manipulation via request parameters. Unfortunately, the correction wasn’t sufficient.
Struts2 provides a mapping between Web parameters and Java methods. So an attacker could invoke a specific method on a remote Java server by specifying it in a URL. All Java objects have a getClass() method, which returns the object’s Class (this object represents classes). Every Class has a ClassLoader, which is the class that loaded the initial class; an attacker could access the ClassLoader using the Class.getClassLoader() method.

Impact
An unauthenticated attacker could manipulate the ClassLoader into disclosing private Class information or possibly load a malicious class file.

Solution
Update

The Apache Struts group has released Struts 2.3.16.2 as a "General Availability" release to address this vulnerability. The Apache Struts group is advising all developers to update.
The vendor has stated the following workaround:

A security fix release fully addressing this issue is in preparation and will be released as soon as possible.

Once the release is available, all Struts2 users are strongly recommended to update their installations.

In your struts.xml, replace all custom references to params-interceptor with the following code, especially regarding the class-pattern found at the beginning of the excludeParams list:

<interceptor-ref name="params">
  <param name="excludeParams">(.*\.|^|.*|\[(‘|"))(c|C)lass(\.|(‘|")]|\[).*,^dojo\..*,^struts\..*,^session\..*,^request\..*,^application\..*,^servlet(Request|Response)\..*,^parameters\..*,^action:.*,^method:.*</param>
</interceptor-ref>

If you are using default interceptor stacks packaged in struts-default.xml, change your parent packages to a customized secured configuration as in the following example. Given you are using defaultStack so far, change your packages from

<package name="default" namespace="/" extends="struts-default">
   <default-interceptor-ref name="defaultStack" />
   …
   …
</package>

to

<package name="default" namespace="/" extends="struts-default">
   <interceptors>
       <interceptor-stack name="secureDefaultStack">
           <interceptor-ref name="defaultStack">
               <param name="params.excludeParams">(.*\.|^|.*|\[(‘|"))(c|C)lass(\.|(‘|")]|\[).*,^dojo\..*,^struts\..*,^session\..*,^request\..*,^application\..*,^servlet(Request|Response)\..*,^parameters\..*,^action:.*,^method:.*</param>
           </interceptor-ref>
       </interceptor-stack>
   </interceptors>

   <default-interceptor-ref name="secureDefaultStack" />
   …
</package>

Vendor Information (Learn More)

VendorStatusDate NotifiedDate UpdatedApache StrutsAffected-25 Apr 2014If you are a vendor and your product is affected, let
us know.

CVSS Metrics (Learn More)

Group
Score
Vector

Base
5.0
AV:N/AC:L/Au:N/C:P/I:–/A:–

Temporal
4.3
E:POC/RL:W/RC:C

Environmental
3.2
CDP:ND/TD:M/CR:ND/IR:ND/AR:ND

References

http://struts.apache.org/announce.html#a20140424
http://blog.trendmicro.com/trendlabs-security-intelligence/chinese-underground-creates-tool-exploiting-apache-struts-vulnerability/

Credit

This vulnerability was publicly reported by Apache Struts2.
This document was written by Michael Orlando and David Svoboda.

Other Information

CVE IDs:
CVE-2014-0094

Date Public:
24 Apr 2014

Date First Published:
25 Apr 2014

Date Last Updated:
28 Apr 2014

Document Revision:
11

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