CVE-2026-93008 in Ceph Storage
Summary
by MITRE • 10/29/2026
A flaw was found in dnsmasq. When following a CNAME in a DNS response, the resolver can cache records for the CNAME target without checking that those records belong to the responding server's authorized zone. In split-DNS deployments that send some domains to a specific upstream, an attacker who controls that upstream can inject cache entries for unrelated names. Later clients may then receive attacker-chosen addresses for those names.
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Analysis
by VulDB Data Team • 10/29/2026
The vulnerability identified in dnsmasq represents a critical failure in DNS zone validation logic during the resolution of Canonical Name records. In standard DNS operations, when a resolver encounters a CNAME record pointing to another domain name, it must recursively query that target address to retrieve the final A or AAAA record. The core technical flaw lies in the fact that dnsmasq fails to verify whether these subsequently cached records for the CNAME target fall within the authorized zone of the responding upstream server. This oversight allows an attacker who controls a specific upstream DNS server, particularly in split-DNS deployments where certain domains are routed through designated resolvers, to inject arbitrary cache entries. By exploiting this lack of boundary enforcement, the malicious upstream can associate unrelated domain names with IP addresses controlled by the attacker, effectively poisoning the local resolver's cache without proper authorization checks for those specific target records.
The operational impact of this vulnerability is significant, as it enables DNS cache poisoning attacks that can redirect legitimate traffic to malicious infrastructure. When a client queries dnsmasq for a name that triggers the flawed CNAME resolution path, the resolver may return an attacker-chosen IP address instead of the correct one. This misdirection facilitates various downstream attacks including phishing campaigns where users are directed to fraudulent login pages, man-in-the-middle attacks allowing interception and modification of unencrypted traffic, or malware distribution via compromised download links. The severity is amplified in environments utilizing split-DNS architectures because these setups often rely on specific upstream servers for internal domain resolution, creating a trusted relationship that the vulnerability exploits by bypassing zone boundary validation.
From an industry standards perspective, this flaw aligns with CWE-20 Improper Input Validation and CWE-787 Out-of-bounds Write if considered in terms of memory safety, though more accurately it reflects CWE-913 Control of Resource Through Uncontrolled Frequency or CWE-645 Relative Path Traversal concepts applied to DNS zone boundaries. In the context of MITRE ATT&CK, this vulnerability facilitates techniques associated with T1071 Application Layer Protocol: Web Protocols for initial access and potentially T1078 Valid Accounts if used in conjunction with credential harvesting after redirection. The failure to validate that cached records belong to authorized zones is a fundamental breach of DNS security principles outlined in RFC 2308 regarding negative caching, although this specific issue pertains more closely to the integrity checks required during positive resolution chains as described in broader DNSSEC validation contexts which dnsmasq may not fully enforce by default.
Mitigation strategies must focus on updating the software and adjusting configuration parameters where possible. The primary remediation is to apply the latest patches provided by the dnsmasq maintainers that address this specific logic error in CNAME handling. Administrators should also consider implementing DNSSEC validation if supported by their infrastructure, as cryptographic signatures would prevent an attacker from injecting forged records even if they control the upstream server. Additionally, reviewing split-DNS configurations to ensure that only trusted and strictly monitored upstream servers are used for critical domain resolutions can reduce the attack surface. Network-level monitoring tools should be deployed to detect anomalous DNS query patterns or unexpected cache entries that do not align with known authoritative sources, providing an additional layer of defense against exploitation attempts.