# CVE-2026-42272: dadrus Heimdall authorization bypass via case-sensitive URL encoding

Source: https://junglewise.ai/threats/cve-2026-42272-dadrus-heimdall-authorization-bypass-via-case-sensitive-url  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-08. Updated: 2026-05-12  
License: CC BY 4.0 with a link back

CVE-2026-42272 · Severity: high · CVSS 4 · Published 2026-05-08

Heimdall, an identity-aware proxy used to control access to web services, contains a flaw in how it processes web addresses. By using lowercase characters in certain parts of a web link, an attacker can trick the proxy into ignoring security rules while the backend service still processes the request. This can allow unauthorized users to access restricted data or administrative functions if the system is not configured with strict 'deny-by-default' rules.

Technologies: [Dadrus Heimdall](https://junglewise.ai/threats/technologies/heimdall), [github.com/dadrus/heimdall (Go)](https://junglewise.ai/threats/technologies/github-com-dadrus-heimdall). Vendors: [Dadrus](https://junglewise.ai/threats/vendors/dadrus), [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-42272 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42272 being exploited in the wild.

**How severe is CVE-2026-42272?** High severity, with a CVSS score of 4, published 8 May 2026.

**Which products and versions are affected?** Dadrus Heimdall < 0.17.14; github.com/dadrus/heimdall (Go) < 0.17.14, SEMVER:introduced=0,fixed=0.17.14.

**Is there a fix for CVE-2026-42272?** Yes. github.com/dadrus/heimdall (Go): upgrade to 0.17.14 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-42272 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-42272?** Check whether you run Dadrus Heimdall or github.com/dadrus/heimdall (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/dadrus/heimdall (Go): upgrade to 0.17.14 or later

  ```sh
  go get github.com/dadrus/heimdall@v0.17.14
  ```


## Technical details

Heimdall improperly handles percent-encoded slashes by treating '%2F' and '%2f' differently, despite the specification requiring case-insensitivity. When 'allow_encoded_slashes' is set to 'off' (default), lowercase '%2f' is not recognized or rejected, causing the request to bypass specific path-based rules (e.g., /admin/**). If a permissive default rule is active, the request is forwarded to upstream services which may interpret '%2f' as a valid path separator, leading to an interpretation conflict and authorization bypass. This vulnerability is particularly impactful in configurations where secure defaults have been explicitly disabled. The issue is resolved in version 0.17.14.

## Affected products

- dadrus Heimdall < 0.17.14

## Identifiers

- CVE-2026-42272
- GHSA-43jv-5j4x-qv67
- GO-2026-5108

## Timeline

- 2026-04-21: disclosed: Advisory published by maintainer
- 2026-04-25: advisory: GHSA published
- 2026-05-08: advisory: NVD published CVE-2026-42272
- 2026-04-21: patched: Version 0.17.14 released

## References

- [https://github.com/dadrus/heimdall/security/advisories/GHSA-43jv-5j4x-qv67](https://github.com/dadrus/heimdall/security/advisories/GHSA-43jv-5j4x-qv67)
- [https://github.com/dadrus/heimdall/pull/3207](https://github.com/dadrus/heimdall/pull/3207)
- [https://github.com/dadrus/heimdall/commit/8b0de6aba23a047cfee3081df878271bb17f4351](https://github.com/dadrus/heimdall/commit/8b0de6aba23a047cfee3081df878271bb17f4351)
- [https://github.com/dadrus/heimdall/releases/tag/v0.17.14](https://github.com/dadrus/heimdall/releases/tag/v0.17.14)
- [https://api.github.com/repos/dadrus/heimdall/security-advisories/GHSA-43jv-5j4x-qv67](https://api.github.com/repos/dadrus/heimdall/security-advisories/GHSA-43jv-5j4x-qv67)

## Related threats

- [Heimdall IP spoofing via unvalidated forwarding headers](https://junglewise.ai/threats/cve-2026-57210-heimdall-ip-spoofing-via-unvalidated-forwarding-headers)
- [Heimdall Forwarded header injection in proxy mode](https://junglewise.ai/threats/cve-2026-57209-heimdall-forwarded-header-injection-via-unsanitized-host-header)
- [dadrus Heimdall authorization bypass via path normalization mismatch](https://junglewise.ai/threats/cve-2026-42274-dadrus-heimdall-authorization-bypass-via-path-normalization)
- [Dadrus Heimdall case-sensitive host matching policy bypass](https://junglewise.ai/threats/cve-2026-42273-dadrus-heimdall-case-sensitive-host-matching-policy-bypass)
- [GO-2026-4742 - Heimdall: Path received via Envoy gRPC corrupted when containing query string in github.com/dadrus/heimdall](https://junglewise.ai/threats/cve-2026-32811-heimdall-path-received-via-envoy-grpc-corrupted-when-containing)