CVE-2006-2842 in SquirrelMail
Summary
by MITRE
** DISPUTED ** PHP remote file inclusion vulnerability in functions/plugin.php in SquirrelMail 1.4.6 and earlier, if register_globals is enabled and magic_quotes_gpc is disabled, allows remote attackers to execute arbitrary PHP code via a URL in the plugins array parameter. NOTE: this issue has been disputed by third parties, who state that Squirrelmail provides prominent warnings to the administrator when register_globals is enabled. Since the varieties of administrator negligence are uncountable, perhaps this type of issue should not be included in CVE. However, the original developer has posted a security advisory, so there might be relevant real-world environments under which this vulnerability is applicable.
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Analysis
by VulDB Data Team • 06/21/2025
The vulnerability described in CVE-2006-2842 represents a critical remote file inclusion flaw within the SquirrelMail webmail application version 1.4.6 and earlier. This security weakness resides in the functions/plugin.php file and specifically exploits the dangerous combination of PHP configuration settings that were common in older web server environments. The vulnerability operates under the premise that when register_globals is enabled and magic_quotes_gpc is disabled, an attacker can manipulate the plugins array parameter to include malicious URLs that will be executed on the target server. This creates a pathway for arbitrary code execution that fundamentally compromises the server's integrity and can lead to complete system takeover.
The technical mechanism behind this vulnerability stems from improper input validation and sanitization within the SquirrelMail application's plugin handling mechanism. When register_globals is enabled, PHP automatically creates global variables from request data, effectively bypassing normal variable scope rules. Combined with the absence of magic_quotes_gpc protection, which normally escapes special characters in GET, POST, and COOKIE data, the application becomes vulnerable to injection attacks. The plugins array parameter in the affected code does not properly validate or sanitize external input, allowing an attacker to inject malicious URLs that get included and executed as PHP code. This vulnerability directly maps to CWE-94, which describes "Improper Control of Generation of Code ('Code Injection')" and specifically relates to the improper handling of dynamic code execution contexts.
The operational impact of this vulnerability extends far beyond simple data theft or service disruption. An attacker who successfully exploits this vulnerability can execute arbitrary commands on the compromised server with the privileges of the web server process. This typically translates to full access to the server's file system, the ability to install backdoors, exfiltrate sensitive data, and potentially escalate privileges to gain root access on the underlying operating system. The implications are particularly severe in shared hosting environments where multiple users might be running on the same server, as this vulnerability could allow one compromised user to affect others. According to ATT&CK framework, this vulnerability corresponds to T1059.007 for "Command and Scripting Interpreter: PowerShell" and T1078.004 for "Valid Accounts: Default Accounts" since the exploitation often leads to privilege escalation and lateral movement within compromised networks.
The disputed nature of this CVE reflects the complex relationship between theoretical security flaws and real-world deployment conditions. While third parties argue that SquirrelMail's security advisory prominently warns administrators about the dangers of enabling register_globals, the vulnerability remains relevant in environments where such warnings are ignored or bypassed. This situation highlights the fundamental principle that security advisories are only as effective as their implementation, and that configuration vulnerabilities often persist in production environments due to administrator negligence or legacy system constraints. Organizations running older versions of SquirrelMail with insecure PHP configurations remain at risk, particularly in environments where security hardening practices are not rigorously enforced. The vulnerability demonstrates the critical importance of proper security configuration management and the dangers of relying on application-level protections when underlying system configurations are insecure.
Mitigation strategies for this vulnerability must address both the immediate exposure and underlying systemic issues. The most effective immediate solution involves disabling register_globals in PHP configuration settings and enabling magic_quotes_gpc, though the latter is deprecated in modern PHP versions. Administrators should also upgrade to patched versions of SquirrelMail where available, as the vulnerability was addressed in subsequent releases. Network-level protections such as web application firewalls can provide additional defense-in-depth, though they cannot substitute for proper configuration hardening. Regular security audits and configuration reviews should be conducted to ensure that dangerous PHP settings are not enabled in production environments. The vulnerability serves as a reminder that security cannot be achieved through application-level fixes alone, but requires comprehensive security practices including proper system configuration, regular updates, and security awareness training for administrators.