CVE-2018-19858 in PrinceXML
Summary
by MITRE
PrinceXML, versions 10 and below, is vulnerable to XXE due to the lack of protection against external entities. If an attacker passes HTML referencing an XML file (e.g., in an IFRAME element), PrinceXML will fetch the XML and parse it, thus giving an attacker file-read access and full-fledged SSRF.
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Analysis
by VulDB Data Team • 05/06/2020
PrinceXML version 10 and earlier contains a critical vulnerability classified as XML External Entity (XXE) that stems from insufficient protection against external entity resolution during XML parsing operations. This flaw exists within the software's processing of HTML content that references external XML files through mechanisms such as iframe elements, creating a pathway for malicious actors to exploit the system's XML parser. The vulnerability is particularly dangerous because it allows attackers to leverage the application's XML processing capabilities to perform unauthorized file system operations and server-side request forgery attacks.
The technical implementation of this vulnerability occurs when PrinceXML processes HTML content containing embedded XML references, specifically through the use of iframe elements that point to external XML resources. When the system encounters such references, it automatically fetches and parses the referenced XML files without proper validation or sanitization of external entity declarations. This behavior creates a direct attack vector where malicious entities can specify external resources that the parser will attempt to resolve, leading to unauthorized file access and potential information disclosure. The vulnerability operates at the core parsing layer of the application, making it particularly challenging to mitigate without comprehensive input validation.
The operational impact of this XXE vulnerability extends beyond simple information disclosure to encompass full server-side request forgery capabilities and unauthorized file system access. Attackers can leverage this vulnerability to read arbitrary files from the server's file system, potentially accessing sensitive configuration files, database credentials, or other confidential data. Additionally, the SSRF component allows attackers to make internal network requests that would otherwise be restricted, potentially enabling them to probe internal services, access backend systems, or even exfiltrate data from internal networks. This makes the vulnerability particularly dangerous in environments where internal network services are not properly isolated or secured.
Organizations using PrinceXML versions 10 and below should immediately implement mitigations to address this XXE vulnerability. The primary recommendation involves disabling external entity resolution in XML parsers and implementing strict input validation for all HTML content that may reference external resources. Security practitioners should consider implementing XML parser configurations that prohibit external entity resolution and restrict access to local files through proper sandboxing mechanisms. Additionally, network-level controls such as firewalls and access control lists should be configured to limit outbound connections from the PrinceXML processing environment to prevent potential SSRF exploitation. The vulnerability aligns with CWE-611 (Improper Restriction of XML External Entity Reference) and represents a significant risk under ATT&CK technique T1071.004 (Application Layer Protocol: DNS) and T1105 (Ingress Tool Transfer) when exploited for information gathering and lateral movement. Organizations should prioritize upgrading to PrinceXML version 11 or later, which includes proper XXE protection mechanisms and enhanced XML parsing security controls.