CVE-2021-44556 in digger
Summary
by MITRE • 12/08/2021
National Library of the Netherlands digger < 6697d1269d981e35e11f240725b16401b5ce3db5 is affected by a XML External Entity (XXE) vulnerability. Since XML parsing resolves external entities, a malicious XML stream could leak internal files and/or cause a DoS.
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Analysis
by VulDB Data Team • 12/11/2021
The vulnerability identified as CVE-2021-44556 affects the National Library of the Netherlands digger software, specifically versions prior to commit 6697d1269d981e35e11f240725b16401b5ce3db5. This represents a critical XML External Entity processing flaw that fundamentally undermines the security posture of the system. The digger software, designed for harvesting and processing digital content from various sources, processes XML data extensively during its operations. When the system parses XML documents without proper safeguards against external entity resolution, it becomes vulnerable to exploitation through maliciously crafted XML streams that can trigger unauthorized data access or service disruption.
The technical flaw stems from inadequate input validation and XML parser configuration within the digger application. When the software encounters XML content containing external entity declarations, it automatically resolves these references without proper authorization checks. This behavior aligns with CWE-611, which specifically addresses improper restriction of XML external entity reference, making it susceptible to both information disclosure and denial of service attacks. The vulnerability manifests when the application processes XML data from untrusted sources, allowing attackers to craft payloads that reference internal system resources through external entity declarations.
The operational impact of this vulnerability extends beyond simple data leakage, as it can enable attackers to perform reconnaissance activities against internal systems and potentially cause service disruption. An attacker could exploit this vulnerability to access sensitive internal files, configuration data, or system resources that should remain protected. The denial of service component of this vulnerability could be leveraged to disrupt the normal operation of the digger service, impacting the library's ability to harvest and process digital content. This vulnerability particularly affects systems where the digger operates in environments with limited network segmentation, as the attack surface expands to include internal network resources.
Mitigation strategies should focus on implementing proper XML parser configuration to disable external entity resolution and parameter entity expansion. The most effective approach involves configuring the XML parser to reject external entity declarations entirely, which aligns with ATT&CK technique T1213.002 for data from information repositories. Organizations should also implement input validation and sanitization for all XML processing components, ensuring that only well-formed, trusted XML content is processed. Additionally, network segmentation and access controls should be strengthened to limit the potential impact of successful exploitation, while regular security updates and patch management procedures should be enforced to prevent similar vulnerabilities from emerging in future versions of the software.