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Heimdall has an authorization bypass via path normalization mismatch

High severity GitHub Reviewed Published Apr 21, 2026 in dadrus/heimdall • Updated Apr 25, 2026

Package

gomod github.com/dadrus/heimdall (Go)

Affected versions

< 0.17.14

Patched versions

0.17.14

Description

Summary

Heimdall performs rule matching on the raw (non-normalized) request path, while downstream components may normalize dot-segments according to RFC 3986, Section 6.2.2.3. This discrepancy can result in heimdall authorizing a request for one path (e.g., /user/../admin, or URL-encoded variants such as /user/%2e%2e/admin or /user/%2e%2e%2fadmin. The latter would require the allow_encoded_slashes option to be set to on or no_decode.) while the downstream ultimately processes a different, normalized path (/admin).

Details

This vulnerability can be exploited by an adversary if rule matching is performed using free (named or unnamed) wildcards without further constraints, as shown in the example snippets below.

id: rule-1
match:
  routes:
    - path: /user/**
execute: # configured to require authentication and authorization
  # ...
id: rule-2
match:
  routes:
    - path: /public/**
execute: # configured to allow anonymous access
  # ...

If an adversary sends a request to /public/../user/whatever, rule-2 will be matched and executed. The downstream service may, however, normalize the request path and interpret it as /user/whatever.

Impact

Bypass of access control policies enforced by heimdall may lead to the following consequences:

  • Access to or modification of data that should be restricted
  • Invocation of functionality that is expected to require authentication or authorization
  • In certain configurations, escalation of privileges depending on the exposed functionality

Workarounds

  • Normalize HTTP paths or reject HTTP paths containing relative path expressions in the layers in front of Heimdall - this is good practice anyway. Some proxies do that by default, such as Traefik; others, such as Envoy, require additional configuration (for Envoy see normalize_path).
  • Include the ID of the rule expected to be executed in the JWT issued by heimdall and check that value in the consuming project's service.

References

@dadrus dadrus published to dadrus/heimdall Apr 21, 2026
Published to the GitHub Advisory Database Apr 25, 2026
Reviewed Apr 25, 2026
Last updated Apr 25, 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 None
Availability None
Subsequent System Impact Metrics
Confidentiality High
Integrity High
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:N/VA:N/SC:H/SI:H/SA:N

EPSS score

Weaknesses

Path Traversal: '.../...//'

The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize '.../...//' (doubled triple dot slash) sequences that can resolve to a location that is outside of that directory. Learn more on MITRE.

Interpretation Conflict

Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-3q34-rx83-r6mq

Source code

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