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MEDIUM severity

Zope AccessControl vulnerable to information disclosure through Python string `format` and `format_map` functionsGHSA-pq59-9fq7-m886

MEDIUMFix: zopefoundation/AccessControl@f980450

GHSA-pq59-9fq7-m886 is a medium-severity (CVSS 6.8) CWE-693 vulnerability in accesscontrol. A fix is available for accesscontrol — see the affected versions and patch details below.

Also known asCVE-2026-77401PYSEC-2026-4022
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-pq59-9fq7-m886.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs41th percentile — riskier than 41% of all scored CVEsHighest risk
0.00%0.32%0.65%0.97%0.5%0.5%0.5%Oct 26Nov 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐍accesscontrol

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIaccesscontrolall versions7.4pip install --upgrade 'accesscontrol==7.4'

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for accesscontrol, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update accesscontrol to 7.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-pq59-9fq7-m886 is resolved across your whole dependency graph.

  3. Workarounds

    Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Frequently Asked Questions

### 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`. Affe
O3 Security · Impact-Aware SCA

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Zope AccessControl vulnerable to information disclosure…