# CVE-2026-42273: Heimdall: Case-sensitive host matching may lead to policy bypass

> Attackers can bypass access control policies by exploiting case-sensitive host matching in Heimdall, allowing unauthorized access to protected resources.

- **Severity:** High 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 May 2026
- **Updated:** 8 May 2026
- **Also known as:** GHSA-72h4-mxfc-jx37, GO-2026-5200

## What is CVE-2026-42273?

CVE-2026-42273 is a high-severity authentication bypass vulnerability in dadrus heimdall, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Heimdall is a cloud native Identity Aware Proxy and Access Control Decision service. Prior to version 0.17.14, Heimdall performs host matching in a case-sensitive manner, while HTTP hostnames are case-insensitive. This discrepancy can result in heimdall failing to match a rule for a request host that differs only in letter casing, potentially causing the request to be classified differently than intended. This issue has been patched in version 0.17.14.

Weakness: CWE-436 (Interpretation Conflict), CWE-178 (Improper Handling of Case Sensitivity)

## Which versions are affected by CVE-2026-42273?

3 open source packages ship an affected version, including github.com/dadrus/heimdall.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/dadrus/heimdall` | Go | All versions | 0.17.14 |
| `github.com/dadrus/heimdall` | Go | All versions | 0.17.14 |
| `github.com/dadrus/heimdall` | Go | All versions | 0.17.14 |

## How do I fix CVE-2026-42273?

Upgrade github.com/dadrus/heimdall to 0.17.14 or later.

## Is CVE-2026-42273 being exploited?

There is no known exploitation of CVE-2026-42273 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42273 and fix it if it is affected.

What it is: CVE-2026-42273 is a high-severity authentication bypass vulnerability in dadrus heimdall, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-42273 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/dadrus/heimdall (Go): affected all versions; fixed in 0.17.14
- github.com/dadrus/heimdall (Go): affected all versions; fixed in 0.17.14
- github.com/dadrus/heimdall (Go): affected all versions; fixed in 0.17.14

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-42273/ (Markdown: https://insights.sbomify.com/CVE-2026-42273/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42273
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42273
- OSV: https://osv.dev/vulnerability/CVE-2026-42273

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42273/
Summaries are generated and may contain mistakes; the official description above is the record.