CVE-2026-42272 Heimdall: Case-sensitive handling of URL-encoded slashes may lead to inconsistent path interpretation
Attackers can bypass authorization checks by using lowercase URL-encoded slashes, exploiting inconsistent path interpretation in Heimdall.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42272?
CVE-2026-42272 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 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. This issue has been patched in version 0.17.14.
Which versions are affected by CVE-2026-42272?
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-2026-42272?
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-2026-42272 being exploited?
There is no known exploitation of CVE-2026-42272 in the wild and no public exploit code.
Sources
Also known as GHSA-43jv-5j4x-qv67, GO-2026-5108.