Zope AccessControl vulnerable to information disclosure through Python string format and format_map functions

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.8 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N

EPSS

• CVE-2026-77401: 0.47% estimated exploitation activity in the next 30 days; percentile 40.62 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Python's string format functionality allows someone controlling the format string to "read" objects accessible (recursively) via attribute access and subscription from accessible objects. Those attribute accesses and subscriptions use Python's full blown getattr and getitem, not the policy restricted AccessControl variants getattr and getitem. This can lead to critical information disclosure. The AccessControl package already guards against direct access to the formatting functions on string instances, but these mitigations did not cover subclasses of str. Affected are all users who allow untrusted users to create AccessControl controlled Python code and execute it. Patches A fix was published with version 7.4. Workarounds There is no workaround.

Published by the source

17 Sep 2026, 16:30 UTC

Last modified by the source

1 Oct 2026, 17:56 UTC

Source last checked

26 Oct 2026, 13:52 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-pq59-9fq7-m886

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-pq59-9fq7-m886

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-pq59-9fq7-m886

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# Patch Next advisory brief: CVE-2026-77401

Advisory: Zope AccessControl vulnerable to information disclosure through Python string `format` and `format_map` functions
IDs: CVE-2026-77401, GHSA-pq59-9fq7-m886
Record: https://patchnext.com/advisories/cve-2026-77401 (revision 3, source checked 26 Oct 2026, 13:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: accesscontrol 7.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI accesscontrol: affected < 7.4; fixed in 7.4

## Suggested inspection (read-only)
- `python -m pip show accesscontrol`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on accesscontrol.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-pq59-9fq7-m886 (GitHub-reviewed advisory GHSA-pq59-9fq7-m886 lists affected ranges: PyPI accesscontrol >=0 <7.4)
- Verified: https://osv.dev/vulnerability/GHSA-pq59-9fq7-m886 (OSV record GHSA-pq59-9fq7-m886 lists affected ranges: PyPI accesscontrol >=0 <7.4 (fixed))

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