How severe is GHSA-43jv-5j4x-qv67?

No CVSS score has been assigned to GHSA-43jv-5j4x-qv67 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-43jv-5j4x-qv67?

GHSA-43jv-5j4x-qv67 affects the following packages: github.com/dadrus/heimdall (Go). Ecosystems affected: Go.

How do I fix GHSA-43jv-5j4x-qv67?

Update github.com/dadrus/heimdall to 0.17.14 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-43jv-5j4x-qv67 is resolved across your whole dependency graph.

How do I detect GHSA-43jv-5j4x-qv67 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/dadrus/heimdall, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-43jv-5j4x-qv67 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is GHSA-43jv-5j4x-qv67 actively exploited in the wild?

No public exploit code has been indexed for GHSA-43jv-5j4x-qv67 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-43jv-5j4x-qv67?

GHSA-43jv-5j4x-qv67 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 34th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-43jv-5j4x-qv67?

GHSA-43jv-5j4x-qv67 is classified as CWE-178 (CWE-178), CWE-436 (CWE-436). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-43jv-5j4x-qv67 published, and has it been updated?

GHSA-43jv-5j4x-qv67 was published on April 25, 2026 and was last updated on June 25, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

Heimdall: Case-sensitive handling of URL-encoded slashes may lead to inconsistent path interpretationGHSA-43jv-5j4x-qv67

Fix: dadrus/heimdall#3207

GHSA-43jv-5j4x-qv67 is a CWE-178 vulnerability in github.com/dadrus/heimdall. A fix is available for github.com/dadrus/heimdall — see the affected versions and patch details below.

Also known asCVE-2026-42272GO-2026-5108

Published

Apr 25, 2026

Updated

Jun 25, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-43jv-5j4x-qv67.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs34th percentile — riskier than 34% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐹github.com/dadrus/heimdall

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Summary

Heimdall handles URL-encoded slashes (%2F) in a case-sensitive manner, while percent-encoding is defined to be case-insensitive. As a result, the lowercase equivalent (%2f) is not recognized and therefore not processed as expected when allow_encoded_slashes is set to off (the default setting).

This discrepancy can lead to differences in how request paths are interpreted by heimdall and upstream components, which may result in authorization bypass.

Note: The issue can only lead to unintended access if heimdall is configured with an "allow all" default rule. Since v0.16.0, heimdall enforces secure defaults and refuses to start with such a configuration unless this enforcement is explicitly disabled (e.g. via --insecure-skip-secure-default-rule-enforcement or the broader --insecure flag).

Details

Consider the following rule configuration:

id: rule-1
match:
  routes:
    - path: /admin/**
execute: # configured to require authentication and authorization
  # ...

If an adversary sends a request such as /admin%2fsecret, neither is the above rule matched, nor is the request rejected (as would be expected when allow_encoded_slashes is set to off). Instead, the default rule (if configured) will be executed.

If the configured default rule is overly permissive (e.g. allowing anonymous access), and the upstream service interprets %2f as a path separator, the request may ultimately be processed as /admin/secret.

This results in the request being authorized based on a different path than the one processed by the upstream service, leading to authorization bypass.

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

Developers should not use the --insecure or the --insecure-skip-secure-default-rule-enforcement flags and configure their default rule to implement "deny by default".
Reject HTTP paths containing encoded slashes in the layers in front of heimdall. Some proxies, like e.g., Traefik, do that by default.
Include the ID of the rule expected to be executed in the JWT issued by heimdall and verify that value in the project's service.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/dadrus/heimdall`	all versions	0.17.14`go get github.com/dadrus/heimdall@v0.17.14`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/dadrus/heimdall, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/dadrus/heimdall to 0.17.14 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-43jv-5j4x-qv67 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### Summary Heimdall handles URL-encoded slashes (`%2F`) in a case-sensitive manner, while percent-encoding is defined to be case-insensitive. As a result, the lowercase equivalent (`%2f`) is not recognized and therefore not processed as expected when `allow_encoded_slashes` is set to `off` (the default setting). This discrepancy can lead to differences in how request paths are interpreted by heimdall and upstream components, which may result in authorization bypass. **Note:** The issue can only lead to unintended access if heimdall is configured with an "allow all" default rule. Since v0.1