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AWS Load Balancer Controller cross-kind route precedence allows cross-namespace traffic interception

Moderate
shraddhabang published GHSA-xrm9-7r8w-92r3 Jul 14, 2026

Package

gomod https://github.com/kubernetes-sigs/aws-load-balancer-controller (Go)

Affected versions

v3.4.1

Patched versions

v3.4.2

Description

Impact

AWS Load Balancer Controller is an open source Kubernetes controller that manages AWS Application Load Balancer (ALB) and Network Load Balancer resources using Kubernetes Gateway API objects. An issue exists where, under certain circumstances, conflicting HTTPRoute and GRPCRoute objects attached to a shared Gateway listener are assigned ALB listener rule priorities based on route kind rather than route specificity, allowing cross-namespace traffic interception.

Impact In AWS Load Balancer Controller versions that support both GRPCRoute and HTTPRoute objects on the same Gateway listener, the function responsible for sorting listener rules processed HTTPRoute-derived rules and GRPCRoute-derived rules independently, then placed all HTTPRoute rules before all GRPCRoute rules regardless of specificity. As a result, a catch-all HTTPRoute (e.g., PathPrefix /) would receive ALB listener rule priority 1 and be evaluated before a more specific GRPCRoute (e.g., /Service/Method), intercepting traffic intended for that GRPCRoute.

A user with permission to create or update HTTPRoute objects in their own namespace — with no cluster-admin or AWS credentials required — could create a catch-all HTTPRoute for a hostname served by another namespace's GRPCRoute on a shared Gateway. This would cause the catch-all HTTPRoute to intercept, spoof, or deny traffic intended for the victim namespace's gRPC service.

This issue requires the following preconditions:
A shared Gateway with AllowedRoutes.Namespaces.From set to All, or a namespace selector that includes both the affected and the other namespace.

The user has permission to create or update HTTPRoute objects only within their own namespace.

Impacted versions: <= v3.4.1

Patches

This issue has been addressed in AWS Load Balancer Controller version 3.4.2. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.
Ref: https://github.com/kubernetes-sigs/aws-load-balancer-controller/releases/tag/v3.4.2

Workarounds

Restrict the Gateway listener AllowedRoutes.Namespaces.From field to Same, or configure a restrictive namespace Selector, to prevent untrusted namespaces from attaching routes to a shared Gateway listener.

References

If you have any questions or comments about this advisory, we ask that you contact AWS Security via our vulnerability reporting page or directly via email to aws-security@amazon.com. Please do not create a public GitHub issue.

Acknowledgement

We would like to thank hakuopi for collaborating on this issue through the coordinated vulnerability disclosure process.

Severity

Moderate

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 Present
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality High
Integrity High
Availability High

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:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H

CVE ID

CVE-2026-15738

Weaknesses

Improper Isolation or Compartmentalization

The product does not properly compartmentalize or isolate functionality, processes, or resources that require different privilege levels, rights, or permissions. Learn more on MITRE.