Heimdall: Case-sensitive handling of URL-encoded slashes may lead to inconsistent path interpretation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.8 · 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 · score source

EPSS

• CVE-2026-42272: 0.40% estimated exploitation activity in the next 30 days; percentile 33.87 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 allowencodedslashes 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: 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…

Published by the source

25 Apr 2026, 23:29 UTC

Last modified by the source

12 May 2026, 13:28 UTC

Source last checked

26 Oct 2026, 15:20 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-43jv-5j4x-qv67

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# Patch Next advisory brief: CVE-2026-42272

Advisory: Heimdall: Case-sensitive handling of URL-encoded slashes may lead to inconsistent path interpretation
IDs: CVE-2026-42272, GHSA-43jv-5j4x-qv67
Record: https://patchnext.com/advisories/cve-2026-42272 (revision 1, source checked 26 Oct 2026, 15:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/dadrus/heimdall 0.17.14. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/dadrus/heimdall: affected < 0.17.14; fixed in 0.17.14

## Suggested inspection (read-only)
- Go github.com/dadrus/heimdall: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/dadrus/heimdall.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-43jv-5j4x-qv67 (GitHub-reviewed advisory GHSA-43jv-5j4x-qv67 lists affected ranges: Go github.com/dadrus/heimdall >=0 <0.17.14)

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