CVE-2010-4657 in PHP
Summary
by MITRE
PHP5 before 5.4.4 allows passing invalid utf-8 strings via the xmlTextWriterWriteAttribute, which are then misparsed by libxml2. This results in memory leak into the resulting output.
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Analysis
by VulDB Data Team • 03/04/2025
The vulnerability identified as CVE-2010-4657 represents a critical security flaw in PHP5 versions prior to 5.4.4 that stems from improper handling of UTF-8 encoded strings within the xmlTextWriterWriteAttribute function. This issue specifically affects applications that process XML data through PHP's XML extensions and demonstrates a classic case of input validation failure that can lead to memory corruption and potential information disclosure. The vulnerability operates at the intersection of character encoding handling and XML processing libraries, creating a pathway for malicious actors to exploit memory management issues in the underlying libxml2 library. According to CWE-170, this vulnerability falls under the category of improper handling of potentially invalid input data, while the ATT&CK framework would classify this as a memory corruption technique that could enable further exploitation through information disclosure or denial of service conditions. The flaw occurs when PHP processes invalid UTF-8 sequences through the xmlTextWriterWriteAttribute function, which then passes these malformed sequences to libxml2 for processing. This interaction creates a scenario where the XML writer component fails to properly sanitize or validate UTF-8 input before passing it to the underlying XML processing library, resulting in unexpected behavior during memory allocation and deallocation. The misparsing of UTF-8 strings in this context causes the libxml2 library to allocate memory in unexpected ways, leading to memory leaks where allocated memory regions are not properly freed or returned to the system. These memory leak conditions can accumulate over time, potentially leading to resource exhaustion and system instability, while also providing attackers with information about memory layout that could aid in more sophisticated exploitation attempts. The operational impact of this vulnerability extends beyond simple memory consumption issues, as it can affect the stability of web applications and services that rely on XML processing, particularly those handling user-supplied data through XML APIs or web services. Applications using PHP versions before 5.4.4 that process XML data with user input are particularly susceptible to this vulnerability, as the memory leak conditions can be triggered through carefully crafted invalid UTF-8 sequences in XML attributes. The vulnerability's exploitation potential is enhanced by the fact that it operates at a low level within the XML processing stack, making it difficult to detect through standard application-level security controls. Organizations affected by this vulnerability should prioritize upgrading their PHP installations to version 5.4.4 or later, as this release includes proper UTF-8 validation and sanitization mechanisms that prevent the problematic interaction with libxml2. Additionally, implementing proper input validation at the application level, including UTF-8 encoding verification and sanitization routines, can provide additional defense-in-depth measures. Security monitoring should include detection of unusual memory consumption patterns that might indicate the exploitation of this vulnerability, while network-based intrusion detection systems should be configured to identify malformed UTF-8 sequences in XML traffic that could be indicative of attempted exploitation. The vulnerability serves as a reminder of the importance of proper input validation and the need for comprehensive testing of character encoding handling within XML processing libraries, particularly when dealing with external data sources that may contain malformed or malicious input sequences.