CVE-2026-57209 Heimdall: Forwarded Header Injection via Unsanitized Host Header in Proxy Mode
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-57209?
CVE-2026-57209 is a high-severity vulnerability in dadrus heimdall, published on 23 Oct 2026.
Official description
Heimdall is a cloud native Identity Aware Proxy and Access Control Decision service. Prior to version 0.17.17, when Heimdall operates in proxy mode, it constructs the Forwarded HTTP header after executing the matched rule pipeline by inserting the incoming request's Host header value directly into the header string without sanitizing commas or semicolons. This allows an attacker to inject additional parameters into the Forwarded header, potentially spoofing IP addresses for upstream services. This issue has been patched in version 0.17.17.
Which versions are affected by CVE-2026-57209?
3 open source packages ship an affected version, including github.com/dadrus/heimdall.
| Package | Affected | Fixed in |
|---|---|---|
github.com/dadrus/heimdall Go | All versions | 0.17.17 |
github.com/dadrus/heimdall Go | All versions | 0.17.17 |
github.com/dadrus/heimdall Go | All versions | 0.17.17 |
How do I fix CVE-2026-57209?
Upgrade github.com/dadrus/heimdall to 0.17.17 or later.
Is CVE-2026-57209 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-57209 exists.
Sources
Also known as GHSA-4jgr-pg2m-m988, GO-2026-5125.