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  • S2-057
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Summary

Possible Remote Code Execution when alwaysSelectFullNamespace is true (either by user or a plugin like Convention Plugin) and then: results are used with no namespace and in same time, its upper package have no or wildcard namespace and similar to results, same possibility when using url tag which doesn’t have value and action set and in same time, its upper package have no or wildcard namespace.

Who should read this

All Struts 2 developers and users

Impact of vulnerability

Possible Remote Code Execution when alwaysSelectFullNamespace is true (either by user or a plugin like Convention Plugin) and then: results are used with no namespace and in same time, its upper package have no or wildcard namespace and similar to results, same possibility when using url tag which doesn’t have value and action set and in same time, its upper package have no or wildcard namespace.

Maximum security rating

Critical

Recommendation

Upgrade to Struts 2.3.35 or Struts 2.5.17

Affected Software

Struts 2.0.4 - Struts 2.3.34, Struts 2.5.0 - 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 alwaysSelectFullNamespace is true (either by user or a plugin like Convention Plugin) and then: namespace value isn't set for a result defined in underlying configurations and in same time, its upper package configuration have no or wildcard namespace and same possibility when using url tag which doesn’t have value and action set and in same time, its upper package configuration 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 for your all defined packages. Or, verify that you have set (and always not forgot to set) namespace for your all defined results (if is applicable) and verify that you have set (and always not forgot to set) value or action for all url tags in your JSPs, when their upper package 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.