CVE-2021-32811

Remote Code Execution via Script (Python) objects under Python 3

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 [email protected]

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.

CVE-2021-32811 has a CVSS score of 7.5 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.6.3, 5.3); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

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.

1. What is CVE-2021-32811? CVE-2021-32811 is a high-severity security vulnerability in Zope (pip), affecting versions >= 4.0, < 4.6.3. It is fixed in 4.6.3, 5.3.
2. How severe is CVE-2021-32811? CVE-2021-32811 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of Zope are affected by CVE-2021-32811? Zope (pip) versions >= 4.0, < 4.6.3 is affected.
4. Is there a fix for CVE-2021-32811? Yes. CVE-2021-32811 is fixed in 4.6.3, 5.3. Upgrade to this version or later.
5. Is CVE-2021-32811 exploitable, and should I be worried? Whether CVE-2021-32811 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-32811 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-32811?
   • Upgrade Zope to 4.6.3 or later
   • Upgrade Zope to 5.3 or later

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