CVE-2016-2099 in Communications
Summary
by MITRE
Use-after-free vulnerability in validators/DTD/DTDScanner.cpp in Apache Xerces C++ 3.1.3 and earlier allows context-dependent attackers to have unspecified impact via an invalid character in an XML document.
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Analysis
by VulDB Data Team • 03/05/2020
The CVE-2016-2099 vulnerability represents a critical use-after-free flaw within Apache Xerces C++ library version 3.1.3 and earlier, specifically within the validators/DTD/DTDScanner.cpp component. This vulnerability arises from improper memory management during XML document parsing operations, creating a scenario where freed memory locations may be accessed or reused by subsequent operations. The flaw manifests when the parser encounters an invalid character within an XML document, triggering an unpredictable sequence of memory deallocations followed by potential access patterns that can lead to arbitrary code execution or system instability.
The technical exploitation of this vulnerability occurs through malformed XML input that causes the DTD scanner to process invalid characters in a manner that leads to memory corruption. When the parser encounters such malformed content, it triggers a sequence where memory allocated for parsing state information is freed, but subsequent parsing operations may attempt to access this already-released memory space. This use-after-free condition creates a memory safety violation that can be leveraged by attackers to execute malicious code with the privileges of the affected application. The vulnerability is context-dependent because it requires specific conditions involving XML document structure and parsing state to be triggered, making it more challenging to exploit but still potentially dangerous in environments where XML parsing is performed on untrusted input.
From an operational perspective, this vulnerability presents significant risks to applications that rely on Apache Xerces C++ for XML processing, particularly those handling user-provided or external XML data. The unspecified impact mentioned in the CVE description reflects the potential for various security consequences including denial of service, information disclosure, or remote code execution depending on the specific exploitation scenario and target environment. Systems utilizing this library for XML validation, document processing, or data integration may become vulnerable to attacks that could compromise system integrity and confidentiality. The vulnerability's impact is amplified in web applications, enterprise systems, and any software that performs XML parsing without proper input sanitization, as these environments often process XML data from multiple untrusted sources.
Organizations should prioritize immediate mitigation through upgrading to Apache Xerces C++ version 3.1.4 or later, which contains the necessary patches to address this memory management flaw. Additionally, implementing input validation and sanitization measures at the application level can provide defense-in-depth protection against exploitation attempts. Security monitoring should focus on detecting unusual XML parsing behavior or memory access patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-416, which addresses use-after-free conditions in software implementations, and could potentially map to ATT&CK technique T1203, representing exploitation of memory corruption vulnerabilities for privilege escalation or code execution. Organizations should also consider implementing network segmentation and access controls to limit potential attack vectors and reduce the impact of successful exploitation attempts.