CVE-2016-2073 in libxml2
Summary
by MITRE
The htmlParseNameComplex function in HTMLparser.c in libxml2 allows attackers to cause a denial of service (out-of-bounds read) via a crafted XML document.
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Analysis
by VulDB Data Team • 07/06/2022
The vulnerability identified as CVE-2016-2073 resides within the libxml2 library's HTML parser implementation, specifically within the htmlParseNameComplex function located in HTMLparser.c. This flaw represents a classic out-of-bounds read condition that manifests when processing malformed XML documents. The vulnerability operates at the parsing layer of the XML processing stack, where the parser attempts to extract and validate element names from malformed input. When an attacker crafts a specially designed XML document containing malformed name sequences, the htmlParseNameComplex function fails to properly validate array bounds during its parsing operations, leading to memory access violations that can trigger system instability.
The technical exploitation of this vulnerability occurs through careful manipulation of XML document structure to force the parser into reading memory locations beyond the allocated buffer boundaries. This out-of-bounds read condition can result in unpredictable behavior including application crashes, memory corruption, or potentially more severe consequences depending on the execution environment. The flaw demonstrates poor input validation and boundary checking practices that violate fundamental security principles. From a cybersecurity perspective, this vulnerability aligns with CWE-129, which addresses improper validation of array index values, and represents a classic example of how input sanitization failures can lead to denial of service conditions. The ATT&CK framework categorizes this under privilege escalation and denial of service techniques, as the vulnerability can be leveraged to disrupt services without requiring elevated privileges.
The operational impact of CVE-2016-2073 extends beyond simple service disruption to encompass broader system stability concerns. When exploited, this vulnerability can cause applications utilizing libxml2 to crash repeatedly, leading to service unavailability for legitimate users. The vulnerability is particularly concerning in web applications and services that process untrusted XML input, as it can be easily triggered through common attack vectors such as file uploads, API endpoints, or user-submitted content. Organizations running systems that depend on libxml2 for XML processing are at risk of experiencing cascading failures, especially in environments where XML parsing is performed on behalf of multiple users or in high-volume transaction processing scenarios. The vulnerability's exploitation requires minimal skill and can be automated, making it attractive to attackers seeking to disrupt services or establish persistent access through resource exhaustion attacks.
Mitigation strategies for CVE-2016-2073 primarily focus on immediate patching and input validation improvements. System administrators should prioritize updating libxml2 to versions containing the fix, which typically includes enhanced boundary checking and input validation within the htmlParseNameComplex function. Additionally, implementing strict XML input validation at application layers can provide defense-in-depth protection against malformed documents reaching the parser. Organizations should consider deploying XML firewalls or validation proxies that can filter suspicious input patterns before they reach vulnerable applications. The implementation of memory protection mechanisms such as stack canaries, address space layout randomization, and heap-based buffer overflow protections can provide additional resilience against exploitation attempts. Regular security assessments and vulnerability scanning should include checks for outdated libxml2 installations to prevent exploitation of this and related vulnerabilities. Security monitoring should also track for unusual application crash patterns or service disruptions that might indicate exploitation attempts targeting this specific denial of service condition.