CVE-2021-32811: Remote Code Execution via Script (Python) objects under Python 3
Impact Background: The optional add-on package Products.PythonScripts adds Script (Python) to the list of content items a user can add to the Zope object database. Inside these scripts users can write Python code that is executed when rendered through the web. The code environment in these script objects is limited, it relies on the RestrictedPython package to provide a "safe" subset of Python instructions as well as the AccessControl package that defines security policies for execution in the context of a Zope application.
Recently the AccessControl package was updated to fix a remote code execution security issue. A link to the security advisory is provided in the References section below. The bug tightens the AccessControl security policies for Zope by blocking access to unsafe classes inside the Python string module.
You are only affected if the following are true:
- You use Python 3 for your Zope deployment (Zope 4 on Python 2 is not affected) - You run Zope 4 below version 4.6.3 or Zope 5 below version 5.3 - You have installed the optional Products.PythonScripts add-on package
By default, you need to have the admin-level Zope "Manager" role to add or edit Script (Python) objects through the web. Only sites that allow untrusted users to add/edit these scripts through the web - which would be a very unusual configuration to begin with - are at risk.
Patches The problem has been fixed in AccessControl versions 4.3 and 5.2. Zope releases 4.6.3 and 5.3 now require these new AccessControl releases.
Workarounds A site administrator can restrict adding/editing Script (Python) objects through the web using the standard Zope user/role permission mechanisms. Untrusted users should not be assigned the Zope Manager role and adding/editing these scripts through the web should be restricted to trusted users only. This is the default configuration in Zope.
References AccessControl security advisory GHSA-qcx9-j53g-ccgf
For more information If you have any questions or comments about this advisory: Open an issue in the Zope issue tracker Email us at security@plone.org
Other sources
Zope is an open-source web application server. Zope versions prior to versions 4.6.3 and 5.3 have a remote code execution security issue. In order to be affected, one must use Python 3 for one's Zope deployment, run Zope 4 below version 4.6.3 or Zope 5 below version 5.3, and have the optional Products.PythonScripts add-on package installed. By default, one must have the admin-level Zope "Manager" role to add or edit Script (Python) objects through the web. Only sites that allow untrusted users to add/edit these scripts through the web are at risk. Zope releases 4.6.3 and 5.3 are not vulnerable. As a workaround, a site administrator can restrict adding/editing Script (Python) objects through the web using the standard Zope user/role permission mechanisms. Untrusted users should not be assigned the Zope Manager role and adding/editing these scripts through the web should be restricted to trusted users only. This is the default configuration in Zope.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is CVE-2021-32811?
CVE-2021-32811 is a remote code execution security issue in Zope versions prior to versions 4.6.3 and 5.3.
How does CVE-2021-32811 impact Zope?
CVE-2021-32811 allows attackers to remotely execute code on Zope servers running versions below 4.6.3 (for Zope 4) or 5.3 (for Zope 5).
What is the severity of CVE-2021-32811?
The severity of CVE-2021-32811 is high, with a CVSS score of 7.2.
Which software versions are affected?
Zope Accesscontrol versions 4.0 to 4.3 and versions 5.0 to 5.2, as well as Zope versions 4.0 to 4.6.3 and versions 5.0 to 5.3 are affected.
How can I mitigate CVE-2021-32811?
To mitigate CVE-2021-32811, update your Zope installation to versions 4.6.3 (for Zope 4) or 5.3 (for Zope 5) or newer.