S2-057

Summary

Possible Remote Code Execution when using results with no namespace and in same time, its upper action(s) have no or wildcard namespace. Same possibility when using url tag which doesn’t have value and action set.

Who should read this	All Struts 2 developers and users
Impact of vulnerability	Possible Remote Code Execution when using results with no `namespace` and in same time, its upper action(s) have no or wildcard `namespace`. Same possibility when using `url` tag which doesn’t have `value` and `action` set.
Maximum security rating	Critical
Recommendation	Upgrade to Struts 2.3.35 or Struts 2.5.17
Affected Software	Struts 2.3 - Struts 2.3.34, Struts 2.5 - Struts 2.5.16
Reporter	Man Yue Mo from the Semmle Security Research team
CVE Identifier	CVE-2018-11776

Problem

It is possible to perform a RCE attack when namespace value isn't set for a result defined in underlying configurations and in same time, its upper action(s) configurations have no or wildcard namespace. Same possibility when using url tag which doesn’t have value and action set and in same time, its upper action(s) configurations have no or wildcard namespace.

Solution

Upgrade to Apache Struts version 2.3.35 or 2.5.17.

Backward compatibility

Both 2.3.35 and 2.5.17 versions contain the security fixes only, nothing more. No backward incompatibility issues are expected.

We do get reports that in some cases backward compatibility issues can occur, it is related to usage of ArrayList directly in conversion logic. You should see a WARN in logs that the ArrayList is excluded. In such case please define the below constant in your struts.xml

<constant name="struts.excludedPackageNames" value="
    ognl.,
    javax.,
    freemarker.core.,
    freemarker.template.,
    freemarker.ext.rhino.,
    sun.reflect.,
    javassist.,
    com.opensymphony.xwork2.ognl.,
    com.opensymphony.xwork2.security." 
/>

We are working on a new release to fix that problem.

Workaround

This is a temporal weak workaround. Please upgrade to Apache Struts version 2.3.35 or 2.5.17 ASAP because they also contain critical overall proactive security improvements

Verify that you have set (and always not forgot to set) namespace (if is applicable) for your all defined results in underlying configurations. Also verify that you have set (and always not forgot to set) value or action for all url tags in your JSPs. Both are needed only when their upper action(s) configurations have no or wildcard namespace.

Struts 1

As we do not perform any tests against Struts 1 (Struts 1 was announced EOL) we cannot confirm that this version of Struts is not affected by the vulnerability. An example PoC was using an OGNL expression to perform RCE attack, so you can assume Struts 1 is safe as it doesn't base on OGNL.

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