CVE-2013-4200 in Plone
Summary
by MITRE
The isURLInPortal method in the URLTool class in in_portal.py in Plone 2.1 through 4.1, 4.2.x through 4.2.5, and 4.3.x through 4.3.1 treats URLs starting with a space as a relative URL, which allows remote attackers to bypass the allow_external_login_sites filtering property, redirect users to arbitrary web sites, and conduct phishing attacks via a space before a URL in the "next" parameter to acl_users/credentials_cookie_auth/require_login.
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Analysis
by VulDB Data Team • 04/15/2025
The vulnerability described in CVE-2013-4200 represents a critical security flaw in the Plone content management system that affects versions ranging from 2.1 through 4.1, 4.2.x through 4.2.5, and 4.3.x through 4.3.1. This issue resides within the URLTool class's isURLInPortal method in the in_portal.py file, where the system incorrectly processes URLs that begin with a space character. The flaw stems from improper input validation and URL parsing logic that fails to properly identify absolute URLs when they are prefixed with whitespace characters. This misclassification allows malicious actors to exploit the allow_external_login_sites filtering property, which is designed to restrict external redirects during authentication processes. The vulnerability specifically impacts the authentication flow when users are redirected through the acl_users/credentials_cookie_auth/require_login endpoint, where the "next" parameter controls the post-login destination.
The technical exploitation of this vulnerability leverages the fact that the system treats URLs beginning with spaces as relative paths rather than absolute external URLs. This behavior violates standard URL parsing conventions and creates a bypass mechanism for security controls intended to prevent unauthorized redirects. When an attacker crafts a malicious URL with a leading space character and passes it through the "next" parameter, the system incorrectly evaluates it as an internal portal URL instead of recognizing it as an external resource. This misclassification allows attackers to circumvent the allow_external_login_sites property, which normally restricts redirects to trusted domains only. The vulnerability is particularly dangerous because it can be exploited during the authentication process, where users are redirected to attacker-controlled domains after successful login attempts. This creates an ideal environment for phishing attacks, as users may be unknowingly redirected to malicious sites that appear to be legitimate portal extensions.
The operational impact of CVE-2013-4200 extends beyond simple redirect manipulation to encompass broader security implications for Plone installations. Organizations using affected versions of Plone face significant risks including credential theft, data exfiltration, and user deception through sophisticated phishing campaigns. The vulnerability affects the core authentication mechanism, potentially allowing attackers to harvest user credentials from legitimate login sessions or redirect users to malicious sites that can capture sensitive information. Security controls designed to protect against open redirect vulnerabilities become ineffective due to this flaw, as the system's URL validation logic fails to properly distinguish between internal and external resources. This issue directly violates security principles related to input sanitization and URL validation, creating a pathway for attackers to bypass security boundaries that should prevent external access to portal resources.
The exploitation of this vulnerability aligns with several ATT&CK techniques including T1566 for phishing attacks and T1071 for application layer protocol usage. The flaw demonstrates poor input validation practices that map to CWE-20, which covers "Improper Input Validation" in software security. Organizations should implement immediate mitigations including upgrading to patched versions of Plone, implementing additional URL validation controls, and monitoring for suspicious redirect patterns in authentication logs. The vulnerability also highlights the importance of proper URL parsing and normalization in web applications, particularly those handling authentication flows and user redirects. Security teams should consider implementing additional controls such as explicit URL validation routines that strip leading whitespace or reject URLs with non-standard formatting. The affected versions of Plone require immediate patching to address this vulnerability, as the flaw exists in the core authentication and authorization mechanisms that are critical to system security. Organizations should also review their external login site configurations to ensure that the allow_external_login_sites property is properly enforced and that no bypass mechanisms exist for malformed URLs.