CVE-2026-77401: Zope AccessControl: Information disclosure through Python string `format` and `format_map` functions

Vulnerability summary

CVE-2026-77401 is a medium (CVSS 6.8) Protection Mechanism Failure vulnerability in zopefoundation accesscontrol. EPSS estimates a 0.47% chance of exploitation in the next 30 days, higher than 40.6% of scored vulnerabilities.

Timeline

1. 16-09-2026
   PublishedVulnerability first disclosed.
2. 16-09-2026
   Last modifiedVulnerability information updated.

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.

• CWE-693Protection Mechanism FailureThe product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.