CVE-2006-4433 in PHP
Summary
by MITRE
PHP before 4.4.3 and 5.x before 5.1.4 does not limit the character set of the session identifier (PHPSESSID) for third party session handlers, which might make it easier for remote attackers to exploit other vulnerabilities by inserting PHP code into the PHPSESSID, which is stored in the session file. NOTE: it could be argued that this not a vulnerability in PHP itself, rather a design limitation that enables certain attacks against session handlers that do not account for this limitation.
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Analysis
by VulDB Data Team • 08/14/2019
This vulnerability in PHP affects versions prior to 4.4.3 and 5.1.4, specifically targeting third party session handlers that fail to properly validate session identifier character sets. The flaw lies in the lack of input sanitization for the PHPSESSID cookie value, which allows attackers to inject arbitrary characters including potentially malicious PHP code sequences. When session handlers store these identifiers without proper validation, the encoded content can be interpreted as executable code during session processing, creating a pathway for code injection attacks.
The technical implementation of this vulnerability stems from PHP's session management architecture where session identifiers are directly used as file names or storage keys without adequate sanitization. Third party session handlers that store session data in filesystem locations or other persistent storage mechanisms become vulnerable when they use the raw session identifier value without proper character validation. This design limitation creates a scenario where attackers can craft session identifiers containing shell metacharacters or PHP code sequences that get executed when the session data is processed.
From an operational perspective, this vulnerability significantly increases the attack surface for remote code execution against applications using vulnerable PHP versions. Attackers can leverage this weakness to bypass traditional security controls and execute arbitrary commands on the server, particularly when combined with other vulnerabilities or when the session storage mechanism allows for code interpretation. The impact extends beyond simple session hijacking to full system compromise, especially in environments where session data is stored in locations that support code execution or where session handlers are configured to interpret stored content.
The vulnerability aligns with CWE-77 and CWE-94 categories, representing weaknesses in input validation and code injection that can be exploited through session management flaws. It also maps to ATT&CK techniques such as T1190 for exploit public-facing application and T1059 for command and scripting interpreter, as attackers can use this vulnerability to execute code through session identifier manipulation. The attack vector typically involves crafting malicious session identifiers and submitting them through HTTP requests, with the session handler storing and potentially executing the injected content during subsequent session processing.
Mitigation strategies include upgrading to PHP versions 4.4.3 or 5.1.4 and later where proper character validation has been implemented, configuring session handlers to sanitize input before storage, and implementing proper input validation for session identifiers at the application level. Organizations should also review their session storage mechanisms to ensure they do not interpret stored session data as executable code, and consider implementing additional monitoring for unusual session identifier patterns that might indicate exploitation attempts.