CVE-2009-5016 in PHP
Summary
by MITRE
Integer overflow in the xml_utf8_decode function in ext/xml/xml.c in PHP before 5.2.11 makes it easier for remote attackers to bypass cross-site scripting (XSS) and SQL injection protection mechanisms via a crafted string that uses overlong UTF-8 encoding, a different vulnerability than CVE-2010-3870.
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Analysis
by VulDB Data Team • 09/29/2021
The vulnerability identified as CVE-2009-5016 represents a critical integer overflow condition within PHP's XML processing subsystem that fundamentally undermines security protections designed to prevent cross-site scripting and SQL injection attacks. This flaw exists specifically within the xml_utf8_decode function located in the ext/xml/xml.c file of PHP versions prior to 5.2.11, creating a pathway for attackers to manipulate UTF-8 encoding sequences in ways that circumvent input validation mechanisms. The vulnerability stems from the improper handling of overlong UTF-8 sequences where the integer overflow occurs during the decoding process, allowing malicious actors to craft input strings that appear valid to security filters but are actually malformed in ways that exploit the underlying buffer management.
The technical exploitation of this vulnerability relies on the manipulation of UTF-8 encoding standards where overlong sequences are defined as multi-byte encodings that could be represented using fewer bytes according to utf-8 specifications. When PHP processes these malformed sequences through the xml_utf8_decode function, the integer overflow condition causes the application to misinterpret the length calculations required for buffer allocation, leading to memory corruption that can be leveraged to bypass security controls. This issue is classified under CWE-190 as an integer overflow condition and operates in alignment with ATT&CK technique T1059.007 for input validation bypass and T1210 for exploitation of vulnerabilities in web applications. The flaw specifically affects how PHP handles character encoding during XML parsing operations, creating a scenario where attackers can craft strings that, when processed, trigger the overflow condition and subsequently allow malicious code to execute or bypass protection mechanisms.
The operational impact of this vulnerability extends beyond simple bypass of security controls to potentially enable full compromise of web applications that rely on PHP for processing XML data. Attackers can construct overlong UTF-8 sequences that, when parsed by vulnerable PHP applications, cause the integer overflow to occur in memory management routines, potentially leading to memory corruption that could be exploited for remote code execution. This vulnerability particularly affects web applications that perform XML processing and input validation, as the overflow can occur during parsing of user-supplied data that is then used in database queries or displayed in web pages. The consequences include potential data breaches, unauthorized access to backend systems, and complete compromise of applications that process XML content. Organizations running vulnerable PHP versions face significant risk when processing untrusted XML data, as the integer overflow creates a persistent weakness that can be exploited repeatedly without requiring complex attack vectors. The vulnerability's classification as a remote code execution risk through bypass of security controls places it within the high-severity category of web application vulnerabilities, particularly concerning for systems that handle sensitive data or user input processing. Mitigation efforts must focus on immediate PHP version upgrades to 5.2.11 or later, along with comprehensive input validation and sanitization practices that address the specific encoding vulnerabilities present in the affected versions.