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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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.
Which versions are affected by CVE-2026-42273?
3 open source packages ship an affected version, including github.com/dadrus/heimdall.
| Package | 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.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-42273 being exploited?
There is no known exploitation of CVE-2026-42273 in the wild and no public exploit code.
Sources
Also known as GHSA-72h4-mxfc-jx37, GO-2026-5200.