Apache Software Foundation has recently addressed a critical security vulnerability in Apache Ivy, identified as CVE-2022-46751. The flaw is categorized as an improper restriction of XML External Entity Reference (XXE) vulnerability and an XML Injection (aka Blind XPath Injection) vulnerability. These vulnerabilities affect all versions of Apache Ivy prior to version 2.5.2.


When Apache Ivy, prior to version 2.5.2, processes XML files - such as its own configuration files, Ivy files, or Apache Maven POMs (Project Object Model) - it inadvertently allows downloading external document type definitions (DTDs) and expanding any entity references contained therein when used. This behavior can be exploited by malicious actors to exfiltrate sensitive data, access restricted resources on the machine running Ivy, or cause various disruptions to Ivy's execution.

To mitigate this issue, starting with Apache Ivy 2.5.2, DTD processing is now disabled by default, with the exception of parsing Maven POMs. In this scenario, DTD processing is allowed, but only to include the DTD snippet that ships with Ivy. This change helps maintain compatibility with existing Maven POMs that may not be valid XML files but are still accepted by Maven. Furthermore, users have the option to make these settings more lenient through the introduction of new system properties.

Users of affected Apache Ivy versions can mitigate these vulnerabilities by updating to version 2.5.2 or later. As an alternative, users can also configure Java system properties to restrict external DTD processing, as explained in Oracle's "Java API for XML Processing (JAXP) Security Guide" under the section "JAXP Properties for External Access restrictions."

Here is a code snippet demonstrating the recommended Java system properties to mitigate these vulnerabilities:

System.setProperty("javax.xml.accessExternalDTD", "");
System.setProperty("javax.xml.accessExternalStylesheet", "");
System.setProperty("javax.xml. accessExternalSchema", "");

Original References

1. Apache Ivy Release Notes: https://ant.apache.org/ivy/history/latest-milestone/release-notes-2.5.2.html
2. CVE-2022-46751: https://nvd.nist.gov/vuln/detail/CVE-2022-46751
3. Oracle's "Java API for XML Processing (JAXP) Security Guide": https://docs.oracle.com/en/java/javase/17/security/java-api-xml-processing-jaxp-security-guide.html#GUID-CC14EC93-D30-4AF9-B9BB-31C8C8E3BAF7

Exploit Details

The exploit details for CVE-2022-46751 are currently not publicly disclosed. However, understanding the nature of XXE and XML Injection vulnerabilities can inform users about potential attack scenarios. Attackers typically craft malicious XML documents, which, when processed by vulnerable software, execute unintended actions like data exfiltration or unauthorized access to system resources.

In the context of Apache Ivy, attackers may try to exploit CVE-2022-46751 by submitting a crafted XML file through mechanisms like configuration files, Ivy files, or Apache Maven POMs to trigger the unintended behavior.

To prevent this, update to Apache Ivy 2.5.2 or later, where DTD processing is disabled by default for all but Maven POMs, which only includes the necessary DTD snippet shipped with Ivy. This reduces the attack surface while preserving compatibility with existing Maven POMs. Users can also set the appropriate Java system properties, as mentioned earlier, to further restrict external DTD processing.


Published on: 08/21/2023 07:15:00 UTC
Last modified on: 09/06/2023 15:15:00 UTC