CVE-2017-12627 in Xerces-C
Summary
by MITRE
In Apache Xerces-C XML Parser library before 3.2.1, processing of external DTD paths can result in a null pointer dereference under certain conditions.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability CVE-2017-12627 represents a critical null pointer dereference issue within the Apache Xerces-C XML Parser library affecting versions prior to 3.2.1. This flaw exists in the handling of external Document Type Definition (DTD) paths during XML document processing, creating a potential denial of service condition that can be exploited by malicious actors. The vulnerability manifests when the parser encounters specific external DTD references that trigger improper memory management during the parsing lifecycle. The affected library is widely used across enterprise applications, web services, and security tools that process XML content, making this a significant concern for system administrators and security professionals. The issue stems from inadequate validation of external resource references and improper error handling when processing DTD declarations, particularly when these declarations reference external entities that may not be properly resolved.
The technical implementation of this vulnerability involves the parser's failure to properly validate or sanitize external DTD paths before attempting to access or process them. When an XML document contains external DTD references that point to non-existent or improperly formatted resources, the Xerces-C library fails to handle these conditions gracefully. Instead of returning appropriate error codes or terminating the parsing process safely, the parser attempts to dereference a null pointer that results from the failed resource resolution. This behavior creates a crash condition that can be consistently reproduced through carefully crafted XML input containing malicious external DTD references. The flaw operates at the parser level within the XML processing stack, making it particularly dangerous as it can affect any application that relies on Xerces-C for XML parsing operations. The vulnerability is categorized under CWE-476 as a NULL Pointer Dereference, which is a well-known class of software defects that can lead to system instability and potential exploitation.
The operational impact of CVE-2017-12627 extends beyond simple denial of service conditions, as it can be leveraged by attackers to disrupt critical services and potentially escalate privileges within affected systems. Attackers can craft XML documents that trigger the null pointer dereference by including external DTD references that point to malformed or non-existent resources, causing the parser to crash and terminate the application process. This vulnerability is particularly concerning in web applications and services that accept user-provided XML input without proper sanitization, as it enables remote attackers to perform denial of service attacks against targeted systems. The vulnerability aligns with ATT&CK technique T1499.004 for Network Denial of Service, where attackers can exploit parsing flaws to consume system resources or cause application crashes. Organizations using vulnerable versions of Xerces-C may experience service interruptions, application instability, and potential data loss when this vulnerability is exploited in production environments.
Mitigation strategies for CVE-2017-12627 primarily focus on upgrading to Apache Xerces-C version 3.2.1 or later, which includes proper null pointer checks and enhanced error handling for external DTD processing. System administrators should implement comprehensive patch management procedures to ensure all affected applications are updated promptly, as the vulnerability can be exploited remotely through XML input processing. Additional protective measures include implementing XML input validation and sanitization at application level, configuring firewalls to restrict access to external DTD resources, and monitoring application logs for unusual parsing behavior that may indicate exploitation attempts. Security teams should also consider implementing application whitelisting policies that restrict XML parsing to trusted sources and content types, as well as deploying intrusion detection systems that can identify and block malicious XML payloads targeting this specific vulnerability. The fix addresses the root cause by ensuring proper validation of external resource references and implementing graceful error handling that prevents null pointer dereference conditions during XML parsing operations.