CVE-2015-7941 in libxml2
Summary
by MITRE
libxml2 2.9.2 does not properly stop parsing invalid input, which allows context-dependent attackers to cause a denial of service (out-of-bounds read and libxml2 crash) via crafted XML data to the (1) xmlParseEntityDecl or (2) xmlParseConditionalSections function in parser.c, as demonstrated by non-terminated entities.
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Analysis
by VulDB Data Team • 06/27/2022
The vulnerability identified as CVE-2015-7941 represents a critical flaw in the libxml2 XML parsing library version 2.9.2 that manifests as improper input validation during XML document processing. This weakness specifically affects the xmlParseEntityDecl and xmlParseConditionalSections functions within the parser.c file, creating a scenario where malformed XML data can trigger unexpected behavior in the parsing engine. The root cause stems from the library's failure to adequately terminate parsing operations when encountering invalid or malformed input sequences, leading to unpredictable execution paths that can result in system instability.
The technical implementation of this vulnerability involves the manipulation of XML entity declarations and conditional sections through crafted input data that appears to be valid but contains subtle inconsistencies that confuse the parser's state management. When the xmlParseEntityDecl function processes malformed entity declarations, or when xmlParseConditionalSections encounters improperly structured conditional sections, the parsing logic fails to properly handle the exceptional conditions, resulting in out-of-bounds memory read operations. This flaw falls under the CWE-125 vulnerability category, which specifically addresses out-of-bounds read conditions that can lead to information disclosure and system crashes. The vulnerability operates at the application layer and can be exploited through XML-based inputs that are processed by applications relying on libxml2 for document parsing.
From an operational perspective, this vulnerability creates a significant denial of service risk for systems that process XML data from untrusted sources. Attackers can craft malicious XML documents containing non-terminated entities or improperly structured conditional sections that will cause the libxml2 parser to attempt memory accesses beyond allocated boundaries, ultimately leading to application crashes or system instability. The impact extends beyond simple service interruption as the out-of-bounds read operations can potentially expose sensitive memory contents or facilitate more sophisticated attack vectors if combined with other vulnerabilities. This vulnerability is particularly dangerous in web applications, API endpoints, and any system that accepts XML input from external parties, as it can be exploited to disrupt services without requiring elevated privileges or complex attack chains.
The mitigation strategies for CVE-2015-7941 primarily focus on upgrading to patched versions of libxml2 where the parsing logic has been corrected to properly handle malformed input sequences and terminate parsing operations appropriately. Organizations should implement comprehensive input validation measures that filter or sanitize XML data before processing, particularly when dealing with external inputs that may contain malicious content. Additionally, deploying application-level protections such as input length limits, XML schema validation, and sandboxed parsing environments can reduce the attack surface. Network-level protections including XML firewalls and content filtering systems can provide additional layers of defense. Security teams should also consider implementing monitoring and alerting mechanisms to detect unusual parsing behavior or application crashes that may indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under the T1210 technique for exploiting vulnerabilities in parsing libraries, emphasizing the importance of proper input sanitization and library maintenance in preventing such exploitation scenarios.