CVE-2015-8710 in libxml2
Summary
by MITRE
The htmlParseComment function in HTMLparser.c in libxml2 allows attackers to obtain sensitive information, cause a denial of service (out-of-bounds heap memory access and application crash), or possibly have unspecified other impact via an unclosed HTML comment.
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Analysis
by VulDB Data Team • 07/13/2022
The vulnerability identified as CVE-2015-8710 resides within the htmlParseComment function of libxml2's HTMLparser.c component, representing a critical security flaw that affects numerous applications relying on this widely-used XML and HTML parsing library. This vulnerability manifests when processing HTML content containing unclosed HTML comments, creating a dangerous condition that can be exploited by malicious actors to compromise system integrity and availability. The issue stems from improper handling of malformed HTML input, specifically when the parser encounters comment delimiters without proper closure, leading to unpredictable behavior in the parsing process.
The technical nature of this vulnerability involves out-of-bounds heap memory access, which occurs when the htmlParseComment function attempts to read or write memory locations beyond the allocated buffer boundaries. This memory corruption vulnerability is classified under CWE-125 as an out-of-bounds read condition, where the parser's comment handling mechanism fails to properly validate input boundaries before accessing memory segments. The flaw exists because the function does not adequately check for proper comment closure before proceeding with memory operations, allowing attackers to craft malicious HTML content that triggers memory access violations. When an attacker submits HTML containing an unclosed comment, the parser's internal state becomes corrupted, leading to heap memory access beyond allocated limits and potentially causing application crashes or system instability.
The operational impact of CVE-2015-8710 extends beyond simple denial of service conditions to encompass potential information disclosure and unspecified security consequences that could be leveraged for more sophisticated attacks. Applications utilizing libxml2 for HTML processing are at risk of experiencing application crashes or complete system failures when encountering malformed input, creating significant availability concerns for web services, content management systems, and any platform processing user-generated HTML content. The vulnerability's potential for information disclosure means that attackers could potentially extract sensitive data from memory locations that should remain protected, while the unspecified other impacts suggest the possibility of remote code execution under certain conditions. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under the T1203 category for "Exploitation for Privilege Escalation" and T1499 for "Endpoint Denial of Service," making it particularly dangerous in environments where applications process untrusted HTML input from multiple sources.
Mitigation strategies for CVE-2015-8710 should focus on immediate library updates to versions that contain the patched htmlParseComment function, as the original vulnerability was resolved through proper input validation and boundary checking mechanisms. Organizations should implement comprehensive input sanitization measures that validate and normalize HTML content before processing, particularly focusing on comment delimiters and their proper closure. Network defenders should consider deploying web application firewalls and content filtering solutions that can detect and block malformed HTML content before it reaches vulnerable applications. The remediation process requires careful testing of updated libxml2 versions to ensure compatibility with existing applications, as well as implementing monitoring solutions to detect potential exploitation attempts through unusual memory access patterns or application crash reports. Additionally, developers should adopt secure coding practices that emphasize input validation and boundary checking, particularly when implementing custom HTML parsing functionality, to prevent similar vulnerabilities from emerging in future code implementations.