CVE-2016-4043 in Plone
Summary
by MITRE
Chameleon (five.pt) in Plone 5.0rc1 through 5.1a1 allows remote authenticated users to bypass Restricted Python by leveraging permissions to create or edit templates.
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Analysis
by VulDB Data Team • 09/02/2020
The vulnerability CVE-2016-4043 represents a critical authorization bypass flaw in the Chameleon templating engine component of Plone content management system. This issue affects versions ranging from Plone 5.0rc1 through 5.1a1, where authenticated users can exploit specific permissions to circumvent the Restricted Python execution environment that is designed to prevent arbitrary code execution. The vulnerability stems from insufficient access controls within the template creation and editing functionality, allowing malicious users with appropriate privileges to craft templates that execute unrestricted Python code.
The technical exploitation of this vulnerability occurs through the manipulation of template permissions and the subsequent creation or modification of template files within the Plone system. When users possess the ability to create or edit templates, they can leverage this privilege to inject malicious code that bypasses the normal Restricted Python sandbox mechanisms. This occurs because the system fails to properly validate template content against security policies during the creation or modification process, enabling attackers to introduce code that executes outside the intended restricted environment. The flaw specifically targets the template engine's permission handling logic, where the system does not adequately enforce security boundaries between template creation capabilities and the execution environment.
The operational impact of this vulnerability is severe as it provides attackers with a pathway to execute arbitrary code on the affected Plone server. This capability can lead to complete system compromise, data exfiltration, and potential lateral movement within network environments. An authenticated attacker with template creation privileges can effectively bypass the security model that Plone implements to protect against malicious code execution. The vulnerability is particularly concerning because it allows for privilege escalation and can be exploited by users who should only have limited template editing capabilities. The attack vector requires only authenticated access, making it accessible to users who have been granted basic content management permissions.
Mitigation strategies for CVE-2016-4043 involve implementing strict template validation mechanisms and enhancing permission controls within the Plone system. Organizations should ensure that template creation and editing privileges are restricted to trusted administrators only, and that all template content undergoes rigorous security scanning before deployment. The recommended approach includes upgrading to patched versions of Plone where the vulnerability has been addressed through improved permission validation and template security checks. Additionally, implementing network segmentation and monitoring for unusual template modifications can help detect potential exploitation attempts. This vulnerability aligns with CWE-284, which addresses improper access control, and maps to ATT&CK technique T1059.006 for execution through scripting, demonstrating how template manipulation can serve as a vector for code execution. Organizations should also consider implementing automated security controls that prevent the creation of templates containing potentially dangerous code patterns and establish regular security audits of template repositories.