RestrictedPython Protected Hook Bypass in Argument Validation

Publication date: 2026-07-08

Last updated on: 2026-07-08

Assigner: GitHub, Inc.

Description

RestrictedPython is a tool that helps to define a subset of the Python language which allows to provide a program input into a trusted environment. Prior to 8.3, check_function_argument_names() rejected protected guard hook names for regular, variadic, and keyword-only arguments but omitted positional-only arguments, allowing __getattr__, _getitem_, _write_, or _print_ to be shadowed by a local parameter and bypass the embedding application's access policy. This issue is fixed in version 8.3.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-07-08

Last Modified

2026-07-08

Generated

2026-07-09

AI Q&A

2026-07-09

EPSS Evaluated

N/A

NVD

CVE-2026-55830

Affected Vendors & Products

Vendor	Product	Version / Range
restrictedpython	restrictedpython	8.3

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-184	The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.

Attack-Flow Graph

Executive Summary

This vulnerability exists in RestrictedPython versions prior to 8.3. RestrictedPython is a tool designed to define a subset of the Python language to safely execute code in a trusted environment. The issue arises because the function check_function_argument_names() did not properly reject protected guard hook names for positional-only arguments. This omission allowed certain special names like __getattr__, _getitem_, _write_, or _print_ to be shadowed by local parameters, effectively bypassing the access control policies of the embedding application.

Impact Analysis

The vulnerability can lead to a bypass of the embedding application's access policy, potentially allowing an attacker to execute unauthorized actions or access restricted data within the trusted environment. Given the CVSS base score of 8.3 with high impact on confidentiality, integrity, and low impact on availability, this could result in significant security breaches including data exposure or manipulation.

Mitigation Strategies

To mitigate this vulnerability, upgrade RestrictedPython to version 8.3 or later, where the issue has been fixed.

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