CVE-2026-55830: Complete Sandbox Escape via Positional-Only Arguments in RestrictedPython
Vulnerability ID: CVE-2026-55830
CVSS Score: 8.3
Published: 2026-08-28
A critical security flaw was identified in RestrictedPython prior to version 8.3 where positional-only arguments introduced in Python 3.8 were not properly validated. This allowed an attacker executing code within the sandbox to shadow critical security guards like _write_ and _getattr_, leading to a complete sandbox escape and arbitrary code execution on the underlying server.
TL;DR
Incomplete validation of positional-only arguments in RestrictedPython allowed attackers to shadow security hooks and escape the sandbox.
Technical Details
- CWE ID: CWE-184
- Attack Vector: Network
- CVSS v3.1: 8.3 (High)
- EPSS Score: 0.00401 (Percentile: 33.04%)
- Exploit Status: Proof of Concept (PoC)
- CISA KEV Status: Not Listed
- Impact: Arbitrary Code Execution (ACE) via Sandbox Escape
Affected Systems
- RestrictedPython
- Zope
- Plone
Mitigation Strategies
- Upgrade RestrictedPython to 8.3 or higher
- Implement AST preprocessing to block positional-only parameters containing leading underscores
Remediation Steps:
- Identify all python environments utilizing RestrictedPython.
- Update RestrictedPython dependency to at least version 8.3 using standard package managers.
- Implement defensive AST validation logic in administrative input validation pipelines if legacy versions must remain in use.
- Configure restricted execution environments with minimal container-level permissions.
Read the full report for CVE-2026-55830 on our website for more details including interactive diagrams and full exploit analysis.
Top comments (0)