CVE-2026-42274

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.

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.

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

Kodem intelligence

1. What is CVE-2026-42274? CVE-2026-42274 is a high-severity security vulnerability in github.com/dadrus/heimdall (go), affecting versions < 0.17.14. It is fixed in 0.17.14.
2. Which versions of github.com/dadrus/heimdall are affected by CVE-2026-42274? github.com/dadrus/heimdall (go) versions < 0.17.14 is affected.
3. Is there a fix for CVE-2026-42274? Yes. CVE-2026-42274 is fixed in 0.17.14. Upgrade to this version or later.
4. Is CVE-2026-42274 exploitable, and should I be worried? Whether CVE-2026-42274 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-42274 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-42274? Upgrade github.com/dadrus/heimdall to 0.17.14 or later.