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Fencer Vulns
medium 4.4

CVE-2021-32807 json

Remote Code Execution via unsafe classes in otherwise permitted modules

published 2021-07-30 5 y ago modified 2026-07-09 4 mo ago also GHSA-qcx9-j53g-ccgf , PYSEC-2021-335 , PYSEC-2021-875 , EUVD-2021-0001

cvss
4.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.1%
EPSS 2.1% chance of exploitation in 30 days, percentile 81%
public exploits
0
none known

Summary

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. 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. 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.

Patch / fix

  • pypi accesscontrol 4.3, 5.2
  • pypi zope 4.3, 5.2
  • zope accesscontrol 4.3, 5.2

Exploit prediction

2.11% chance of exploitation in the next 30 days, higher than 81% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 4.4 CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N
NVD 3.1 7.2 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 6.5 AV:N/AC:L/Au:S/C:P/I:P/A:P
GitHub 3.1 4.4 CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
pypi accesscontrol
>=4.0, <4.3
>=5.0, <5.2
4.3
5.2
pypi zope
>=4.0, <4.3
>=5.0, <5.2
4.3
5.2

Affected products

  • zopefoundation AccessControl

Classification

Weakness
  • CWE-915 Improperly Controlled Modification of Dynamically-Determined Object Attributes
  • CWE-1321 Improperly Controlled Modification of Object Prototype Attributes

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.