CVE-2026-77401 Zope AccessControl: Information disclosure through Python string `format` and `format_map` functions
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-77401?
CVE-2026-77401 is a medium-severity vulnerability in zopefoundation AccessControl, published on 16 Sep 2026.
Official description
Zope AccessControl provides a general security framework for use in Zope. Prior to 7.4, applications that allow untrusted users to create and execute AccessControl-controlled Python code do not safely guard str.format and str.format_map when those methods are reached through a str subclass. In both ImplPython.py and cAccessControl.c, Python formatting can recursively access attributes and subscriptions using unrestricted getattr and getitem behavior instead of the policy-restricted getattr and getitem operations. A controlled format string can therefore disclose objects reachable from values available to the formatting operation. This issue is fixed in version 7.4.
Weakness: CWE-693
Which versions are affected by CVE-2026-77401?
3 open source packages ship an affected version, including accesscontrol and AccessControl.
| Package | Affected | Fixed in |
|---|---|---|
accesscontrol PyPI | All versions | 7.4 |
accesscontrol PyPI | All versions | 7.4 |
AccessControl PyPI | All versions | 7.4 |
How do I fix CVE-2026-77401?
Upgrade accesscontrol to 7.4 or later.
Is CVE-2026-77401 being exploited?
There is no known exploitation of CVE-2026-77401 in the wild and no public exploit code.
Sources
Also known as GHSA-pq59-9fq7-m886, PYSEC-2026-4022.