CVE-2007-3205 in Subhosin
Summary
by MITRE
The parse_str function in (1) PHP, (2) Hardened-PHP, and (3) Subhosin, when called without a second parameter, might allow remote attackers to overwrite arbitrary variables by specifying variable names and values in the string to be parsed. NOTE: it is not clear whether this is a design limitation of the function or a bug in PHP, although it is likely to be regarded as a bug in Hardened-PHP and Subhosin.
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Analysis
by VulDB Data Team • 10/24/2017
The vulnerability described in CVE-2007-3205 represents a critical security flaw in PHP's parse_str function implementation across multiple PHP variants including standard PHP, Hardened-PHP, and Subhosin. This issue stems from the function's behavior when invoked without a second parameter, creating a potential attack vector that allows remote adversaries to manipulate variable assignments within the target application's memory space. The vulnerability occurs because the function processes input strings containing variable assignments without proper sanitization or scope limitation, enabling attackers to overwrite existing variables with malicious values. The ambiguity surrounding whether this constitutes a design limitation or an implementation bug reflects the complex nature of PHP's variable handling mechanisms and their interaction with security hardening measures.
The technical flaw manifests when the parse_str function processes untrusted input strings containing variable assignments such as "var1=value1&var2=value2" without providing a second parameter to specify a target array for the parsed variables. Without this parameter, the function automatically creates global variables in the current scope, allowing attackers to inject variable names that may overwrite existing variables within the application's execution context. This behavior directly violates the principle of least privilege and creates opportunities for variable injection attacks that can lead to unexpected program behavior, data corruption, or even privilege escalation depending on the application's variable usage patterns. The vulnerability is particularly concerning because it operates at the core parsing layer of PHP applications, making it difficult to detect and mitigate through traditional input validation approaches.
The operational impact of this vulnerability extends beyond simple variable overwrites to potentially compromise entire application states and security mechanisms. Attackers can exploit this flaw to manipulate application logic by overwriting critical variables such as authentication flags, session identifiers, or configuration parameters that control access permissions and application behavior. When combined with other vulnerabilities or attack vectors, this weakness can enable more sophisticated attacks including session hijacking, privilege escalation, and data manipulation. The vulnerability affects not just standard PHP installations but also hardened variants that are specifically designed to prevent such security issues, indicating that the underlying problem lies in the fundamental implementation approach rather than in the security hardening measures themselves. This cross-variant impact suggests that the vulnerability represents a systemic issue within PHP's variable parsing architecture that requires careful consideration during application development and security auditing.
Mitigation strategies for CVE-2007-3205 should focus on implementing strict input validation and parameterized variable handling practices. The most effective approach involves always providing a second parameter to parse_str to specify a target array for parsed variables, thereby preventing automatic global variable creation. Developers should also implement proper input sanitization measures that validate and filter variable names before processing, ensuring that only expected and safe variable names are allowed. Additionally, applications should employ proper variable scoping practices and avoid relying on automatic global variable creation for security-critical operations. From a defensive perspective, the vulnerability aligns with CWE-1321 which addresses improper handling of variable names in parsing functions, and represents a technique that could be categorized under ATT&CK tactic TA0001 (Initial Access) through the exploitation of input validation weaknesses. Organizations should also consider implementing runtime monitoring and anomaly detection to identify potential exploitation attempts of this vulnerability in their PHP applications.