GHSA-4cc2-g9w2-fhf6: Server-Side Request Forgery in python-zeep via Transitive Schema Resolution

Vulnerability ID: GHSA-4CC2-G9W2-FHF6
CVSS Score: 5.9
Published: 2026-06-19

A regression in python-zeep (versions 4.0.0 through 4.3.2) silently ignores the security configuration designed to block transitive external resource fetches during WSDL and XSD parsing. This defect exposes applications to Server-Side Request Forgery (SSRF) when loading untrusted schemas.

TL;DR

A silent regression in python-zeep versions 4.0.0 to 4.3.2 ignores the forbid_external security setting, allowing remote attackers to trigger unauthenticated SSRF against internal endpoints.

⚠️ Exploit Status: POC

Technical Details

• CWE ID: CWE-918
• Attack Vector: Network
• CVSS v3.1: 5.9 (Medium)
• Impact: Confidentiality High
• Exploit Status: Proof of Concept available
• KEV Status: Not listed

Affected Systems

• Applications implementing python-zeep (zeep) version 4.0.0 through 4.3.2
• zeep: >= 4.0.0, <= 4.3.2 (Fixed in: 4.3.3)

Code Analysis

Commit: 83eb07b

Wire up the forbid_external setting to prevent remote HTTP/HTTPS queries during parsing.

Exploit Details

• GitHub Security Advisory: No description

Mitigation Strategies

• Upgrade python-zeep to version 4.3.3 or higher.
• Explicitly enable the forbid_external=True configuration parameter in python-zeep Settings.
• Enforce network egress filtering to block requests to RFC 1918 addresses and link-local cloud metadata endpoints.

Remediation Steps:

1. Run your package manager update command: pip install --upgrade zeep>=4.3.3
2. Locate client instantiation files in the codebase.
3. Import the Settings class from zeep.
4. Define settings = Settings(forbid_external=True) and pass this object to the Client initializer.

References

• GHSA-4cc2-g9w2-fhf6 Security Advisory

Read the full report for GHSA-4CC2-G9W2-FHF6 on our website for more details including interactive diagrams and full exploit analysis.