CVE-2026-52688 in Recursor
Summary
by MITRE • 07/23/2026
RRSIGs with too few labels can lead to bypass of DNSSEC wildcard validation
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Analysis
by VulDB Data Team • 07/23/2026
This vulnerability involves a critical flaw in DNSSEC wildcard validation mechanisms that can be exploited through improperly constructed RRSIG resource record signatures. The issue arises when RRSIG records contain insufficient label counts relative to the domain name being validated, allowing attackers to bypass the intended security protections. When DNS servers process wildcard expansions, they must validate RRSIG signatures against the appropriate number of labels in the domain hierarchy to ensure proper cryptographic binding between the signature and the data being verified.
The technical flaw stems from an inadequate validation check within DNSSEC processing logic where the system fails to properly verify that RRSIG signatures contain the minimum required number of labels for wildcard matching. This occurs particularly when handling DNS queries for subdomains that should be covered by wildcard records but where the signature's label count does not align with the expected validation parameters. The vulnerability manifests because DNSSEC implementations do not enforce strict label count validation during RRSIG processing, allowing signatures with fewer labels than required to pass validation.
Operational impact of this vulnerability is significant as it undermines the fundamental security guarantees provided by DNSSEC wildcard validation. Attackers can exploit this weakness to perform cache poisoning attacks or bypass legitimate wildcard protections, potentially redirecting traffic to malicious endpoints. The vulnerability affects any DNS server or resolver implementing DNSSEC that properly handles wildcard records, creating a window where unauthorized modifications to DNS data can go undetected while maintaining the appearance of valid cryptographic signatures.
This issue relates to CWE-264 and CWE-310 which address cryptographic weaknesses and improper validation of security tokens. The vulnerability aligns with ATT&CK technique T1485 related to data manipulation and T1071.3 for application layer protocol usage, as it exploits DNS protocol handling and cryptographic validation mechanisms. Organizations should implement immediate mitigations including enforcing strict label count validation in RRSIG processing, updating DNSSEC implementations to properly validate signature parameters, and monitoring for anomalous wildcard resolution patterns that might indicate exploitation attempts.
The fix requires DNSSEC implementations to enforce minimum label requirements for wildcard RRSIG signatures, ensuring that the number of labels in the signature matches or exceeds the expected domain hierarchy for proper validation. This includes implementing comprehensive validation checks during DNSSEC processing that verify signature integrity against the complete domain name structure rather than relying solely on partial label matching. System administrators should also consider deploying monitoring solutions that can detect and alert on RRSIG signatures with anomalous label counts, providing additional defense-in-depth measures against this specific class of vulnerability.