CVE-2021-32807

Remote Code Execution via unsafe classes in otherwise permitted modules

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.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the AccessControl issue tracker
• Email us at [email protected]

The module AccessControl defines security policies for Python code used in restricted code within Zope applications. Restricted code is any code that resides in Zope's object database, such as the contents of Script (Python) objects.

The policies defined in AccessControl severely restrict access to Python modules and only exempt a few that are deemed safe, such as Python's string module. However, full access to the string module also allows access to the class Formatter, which can be overridden and extended within Script (Python) in a way that provides access to other unsafe Python libraries. Those unsafe Python libraries can be used for remote code execution.

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-2021-32807 has a CVSS score of 4.4 (Medium). The vector is network-reachable, high 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 (4.3, 5.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

The problem has been fixed in AccessControl 4.3 and 5.2.
Only AccessControl versions 4 and 5 are vulnerable, and only on Python 3, not Python 2.7.

1. What is CVE-2021-32807? CVE-2021-32807 is a medium-severity security vulnerability in AccessControl (pip), affecting versions >= 4.0, < 4.3. It is fixed in 4.3, 5.2.
2. How severe is CVE-2021-32807? CVE-2021-32807 has a CVSS score of 4.4 (Medium). 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 packages are affected by CVE-2021-32807?
   • AccessControl (pip) (versions >= 4.0, < 4.3)
   • zope (pip) (versions >= 4.0, < 4.3)
4. Is there a fix for CVE-2021-32807? Yes. CVE-2021-32807 is fixed in 4.3, 5.2. Upgrade to this version or later.
5. Is CVE-2021-32807 exploitable, and should I be worried? Whether CVE-2021-32807 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-2021-32807 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-2021-32807?
   • Upgrade AccessControl to 4.3 or later
   • Upgrade AccessControl to 5.2 or later
   • Upgrade zope to 4.3 or later
   • Upgrade zope to 5.2 or later

Other vulnerabilities in AccessControl