CVE-2016-8739: Apache CXF JAX-RS XML External Entity Reference Vulnerability

Background

Apache CXF is an open-source services framework that helps build and develop web services using standard protocols such as SOAP and REST. The JAX-RS module in Apache CXF provides support for building RESTful web services. The vulnerability identified as CVE-2016-8739 affects the JAX-RS module in Apache CXF versions prior to 3.0.12 and 3.1.x prior to 3.1.9. This vulnerability arises due to improper restriction of XML external entity references in the Apache CXF JAX-RS module. The module uses Apache Abdera Parser, which by default expands XML entities, leading to a significant XML External Entity (XXE) risk.

Vulnerability Detail

The vulnerability allows an attacker to exploit XML external entity references, which can result in various security risks. By leveraging this vulnerability, an attacker can read arbitrary files on the server, perform server-side request forgery (SSRF) attacks, or conduct denial-of-service (DoS) attacks. The improper handling of XML entities can lead to the disclosure of sensitive information, unauthorized access to internal resources, or the execution of arbitrary code. This vulnerability has a CVSS score of 7.5, indicating a high severity level.

Workaround

If upgrading to a fixed version is not immediately feasible, a temporary workaround can be implemented by disabling the expansion of XML entities in the Apache CXF JAX-RS module. This can be achieved by modifying the configuration of the module to disable entity expansion. Here is an example of how to disable entity expansion in the Apache CXF JAX-RS module configuration:

<jaxrs:providers>
  <bean class="org.apache.cxf.jaxrs.provider.atom.AtomPojoProvider">
    <property name="expandEntityReferences" value="false"/>

Please note that this workaround may have implications on the functionality of the affected module, and upgrading to a fixed version is strongly recommended.

Conclusion

The Apache CXF JAX-RS XML External Entity Reference vulnerability (CVE-2016-8739) poses a significant risk to applications using affected versions of Apache CXF. It is crucial to upgrade to the fixed versions (3.0.12 or later for the 3.0.x branch, and 3.1.9 or later for the 3.1.x branch) to mitigate this vulnerability. If immediate upgrading is not possible, applying the provided workaround to disable entity expansion can help mitigate the risk temporarily. For further assistance and support in vulnerability remediation, please contact DevNack.com.

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