CVE-2006-5465 in PHP
Summary
by MITRE
Buffer overflow in PHP before 5.2.0 allows remote attackers to execute arbitrary code via crafted UTF-8 inputs to the (1) htmlentities or (2) htmlspecialchars functions.
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Analysis
by VulDB Data Team • 04/26/2026
The vulnerability identified as CVE-2006-5465 represents a critical buffer overflow flaw in PHP versions prior to 5.2.0 that specifically affects the htmlentities and htmlspecialchars functions. This weakness stems from inadequate input validation and memory management when processing UTF-8 encoded character sequences, creating a pathway for remote code execution attacks. The vulnerability operates at the core of PHP's string handling mechanisms, where the functions responsible for converting special characters to HTML entities fail to properly bounds-check input data, leading to memory corruption that can be exploited by malicious actors.
The technical implementation of this flaw occurs when PHP processes UTF-8 encoded strings through the htmlentities and htmlspecialchars functions, which are commonly used to sanitize user input and prevent cross-site scripting attacks. When malformed UTF-8 sequences are passed to these functions, the buffer overflow manifests due to improper handling of multi-byte character boundaries. This vulnerability is particularly dangerous because it leverages the widespread use of these functions in web applications, where they are typically employed to process user-submitted data that may contain maliciously crafted UTF-8 sequences designed to trigger the overflow condition. The flaw falls under CWE-121, which categorizes buffer overflow conditions that occur when insufficient bounds checking is performed during memory operations.
From an operational impact perspective, this vulnerability presents a severe threat to web application security as it allows remote attackers to execute arbitrary code on vulnerable systems without requiring authentication or specific privileges. The attack surface is extensive since the affected functions are commonly used throughout PHP applications for input sanitization, making exploitation relatively straightforward for threat actors who can craft malicious UTF-8 sequences. This vulnerability aligns with ATT&CK technique T1190, which covers the exploitation of vulnerabilities in web applications, and specifically targets the execution phase of the attack lifecycle where adversaries seek to gain control over target systems. The potential consequences include complete system compromise, data exfiltration, and persistence mechanisms being established by attackers who leverage this vulnerability.
The mitigation strategy for CVE-2006-5465 primarily involves upgrading to PHP version 5.2.0 or later, where the buffer overflow has been addressed through improved input validation and memory management. Additionally, administrators should implement strict input sanitization practices and avoid using the vulnerable functions with untrusted input data. Security measures should include regular patch management protocols, web application firewalls that can detect and block suspicious UTF-8 sequences, and comprehensive code reviews to identify other potential instances where similar vulnerabilities might exist in custom applications. Organizations should also consider implementing network segmentation and monitoring solutions to detect anomalous traffic patterns that might indicate exploitation attempts targeting this specific vulnerability. The remediation process must include thorough testing of applications after patching to ensure that the upgrade does not introduce regressions in functionality while effectively closing the security gap that the vulnerability represents.