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Hickory DNS's Record Cache Accepts AUTHORITY-Section NS from Sibling Zone via Parent-Pool Zone-Context Elevation

High severity GitHub Reviewed Published Apr 22, 2026 in hickory-dns/hickory-dns • Updated Apr 30, 2026

Package

hickory-recursor (Rust)

Affected versions

>= 0.24.0, <= 0.25.2
= 0.1

Patched versions

0.26.0

Description

Summary

The Hickory DNS project's experimental hickory-recursor crate's record cache (DnsLru) stores records from DNS responses keyed by each record's own (name, type), not by the query that triggered the response. cache_response() in crates/recursor/src/lib.rs chains ANSWER, AUTHORITY, and ADDITIONAL sections into one record iterator before insertion. The bailiwick filter it applies uses the zone context of the NS pool that serviced the lookup, not the zone being queried.

This creates a cross-zone poisoning path. When Hickory builds the NS pool for attacker.poc. it uses the parent poc. NS pool (ns.zone() = "poc."). If the poc. nameserver under the attacker's control includes in its response's AUTHORITY section a record for a sibling zone like victim.poc. NS ns.evil.poc., the bailiwick check is_subzone("poc.", "victim.poc.") passes (victim.poc. is a subdomain of poc.). The record is stored under (victim.poc., NS) in the shared cache.

Subsequently, any client querying a name in victim.poc. causes Hickory to build its NS pool from the poisoned cache entry, routing queries to the attacker's nameserver (ns.evil.poc.) rather than to the legitimate nameserver for victim.poc.. The legitimate NS for that zone receives zero queries.

This issue is fixed in hickory-resolver 0.26.0 with the recursor feature through an architectural change to response-level caching: responses are stored keyed by the originating query (name, type). A response to (attacker.poc. NS) is stored only under that key and cannot affect the (victim.poc., NS) cache entry.

Hickory DNS believes this issue has been present in all published versions of the experimental hickory-recursor crate, which has now been folded into the hickory-resolver crate under the non-default recursor feature flag. The hickory-recursor crate will not receive any updates going forward and all users should migrate to hickory-resolver with the recursor feature.

Users of the hickory-dns binary configured with the opt-in recursor feature and a configuration acting as a recursive resolver should update to 0.26.0+.

Reporter

Qifan Zhang, Palo Alto Networks

References

@cpu cpu published to hickory-dns/hickory-dns Apr 22, 2026
Published to the GitHub Advisory Database Apr 30, 2026
Reviewed Apr 30, 2026
Last updated Apr 30, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Insufficient Verification of Data Authenticity

The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data. Learn more on MITRE.

Use of Incorrectly-Resolved Name or Reference

The product uses a name or reference to access a resource, but the name/reference resolves to a resource that is outside of the intended control sphere. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-83hf-93m4-rgwq

Source code

Credits

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