CVE-2026-123603
Received Received - Intake

Denial of Service via IPv4-mapped IPv6 Address Evasion in Hickory DNS

Publication date: 2026-11-08

Last updated on: 2026-11-08

Assigner: VulnCheck

Description
hickory-proto and hickory-resolver 0.26.0 before 0.26.2, hickory-server 0.25.0-alpha.1 before 0.26.2, and hickory-recursor 0.25.0-alpha.3 through 0.26.0-alpha.1 fail to canonicalize IPv4-mapped IPv6 addresses when checking deny_answers, deny_server, or AccessControlSet rules. Attackers can use IPv4-mapped addresses to evade answer filtering, trigger queries to denied nameservers, or reach hickory-server library deployments on dual-stack IPv6 sockets from denied clients.

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Meta Information

Published
2026-11-08
Last Modified
2026-11-08
Generated
2026-11-08
AI Q&A
2026-11-08
EPSS Evaluated
N/A
NVD
CVE-2026-123603
EUVD
EUVD-2026-119362

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
hickory proto to 0.26.2 (exc)
hickory resolver to 0.26.2 (exc)
hickory server to 0.26.2 (exc)
hickory recursor From 0.25.0-alpha.3 (inc) to 0.26.0-alpha.1 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-284 The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

Attack-Flow Graph

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Executive Summary

This vulnerability affects hickory-proto, hickory-resolver, hickory-server, and hickory-recursor libraries. It allows attackers to bypass filtering rules by using IPv4-mapped IPv6 addresses. This means systems relying on deny_answers, deny_server, or AccessControlSet rules may incorrectly allow access to restricted resources.

Impact Analysis

Attackers could exploit this to evade security controls, query restricted nameservers, or access hickory-server deployments on dual-stack IPv6 sockets from blocked clients. This could lead to unauthorized data access, service disruption, or further network compromise depending on the system configuration.

Compliance Impact

This vulnerability may lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Organizations using affected hickory libraries could face compliance violations, potential fines, and reputational damage due to inadequate access controls.

Mitigation Strategies

Update hickory-proto, hickory-resolver, hickory-server, and hickory-recursor to versions 0.26.2 or later to address the IPv4-mapped IPv6 address handling issue.

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