CVE-2015-8317 in libxml2
Summary
by MITRE
The xmlParseXMLDecl function in parser.c in libxml2 before 2.9.3 allows context-dependent attackers to obtain sensitive information via an (1) unterminated encoding value or (2) incomplete XML declaration in XML data, which triggers an out-of-bounds heap read.
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Analysis
by VulDB Data Team • 06/28/2022
The vulnerability identified as CVE-2015-8317 resides within the libxml2 library's xmlParseXMLDecl function in the parser.c file, affecting versions prior to 2.9.3. This flaw represents a critical information disclosure vulnerability that arises from improper handling of malformed XML data structures during parsing operations. The vulnerability specifically targets the XML declaration parsing mechanism where the library fails to properly validate input boundaries when processing encoding specifications within XML documents.
The technical implementation of this vulnerability stems from the function's inadequate boundary checking during XML declaration parsing, creating conditions where an attacker can craft malicious XML content that triggers an out-of-bounds heap read operation. When the xmlParseXMLDecl function encounters either an unterminated encoding value or an incomplete XML declaration, it attempts to access memory locations beyond the allocated buffer boundaries, potentially exposing sensitive data from adjacent memory regions. This behavior constitutes a classic heap-based buffer overflow condition that can be exploited to extract confidential information stored in memory.
The operational impact of CVE-2015-8317 extends beyond simple information disclosure, as it can potentially reveal sensitive data including cryptographic keys, user credentials, or system memory contents depending on what information happens to reside in the affected memory regions. Attackers can leverage this vulnerability by constructing specially crafted XML documents that, when processed by vulnerable applications using libxml2, trigger the exploitable code path. The context-dependent nature of this vulnerability means that exploitation requires specific conditions where XML data is being parsed and processed by applications that rely on libxml2, making it particularly dangerous in web applications, XML processing services, or any system that handles untrusted XML input.
This vulnerability maps to CWE-125: Out-of-bounds Read within the Common Weakness Enumeration framework, specifically demonstrating how improper input validation can lead to memory access violations. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1059.007 for XML External Entity processing and T1552 for unsecured credentials exposure, as it can potentially expose sensitive information that would otherwise remain protected. The vulnerability's exploitation requires minimal privileges and can be executed through standard XML processing channels, making it particularly attractive to threat actors seeking to extract sensitive information from systems processing XML content.
Mitigation strategies for CVE-2015-8317 primarily involve upgrading to libxml2 version 2.9.3 or later, which includes proper boundary checking and input validation mechanisms that prevent the out-of-bounds heap read conditions. Organizations should also implement input sanitization measures that validate XML content before processing, particularly focusing on XML declaration parsing and encoding specification validation. Additionally, application-level defenses such as XML schema validation, proper error handling, and memory protection mechanisms can help reduce the attack surface. Network segmentation and monitoring for unusual XML processing patterns may also aid in detecting potential exploitation attempts, while regular security assessments should verify that all XML processing components are properly updated and configured to prevent similar vulnerabilities from persisting in the environment.