# CVE-2026-57210: Heimdall: IP Spoofing via Unvalidated Forwarding Headers


- **Severity:** High 7.0 (`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`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 29 Oct 2026
- **Also known as:** GHSA-38x9-25wx-7fg2, GO-2026-5075

## What is CVE-2026-57210?

CVE-2026-57210 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 the trusted_proxies option is configured, heimdall extracts client IP addresses from the Forwarded (for= parameter) and X-Forwarded-For headers and exposes them as Request.ClientIPAddresses to the rule pipeline. However, extracted values are not validated to be syntactically valid IP addresses. Arbitrary strings, malformed IP literals, and RFC 7239 unknown values and obfuscated identifiers are accepted without further checks. In addition, the Forwarded header parser splits on , and ; without accounting for RFC 7239 quoted strings, which can cause a single quoted value to be parsed as multiple entries, with fragments — including trailing quote characters — treated as independent addresses. This issue has been patched in version 0.17.17.

Weakness: CWE-290 (Authentication Bypass by Spoofing), CWE-20 (Improper Input Validation), CWE-116 (Improper Encoding or Escaping of Output)

## Which versions are affected by CVE-2026-57210?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `https://github.com/dadrus/heimdall` | Go | All versions | 0.17.17 |
| `https://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-2026-57210?

Upgrade https://github.com/dadrus/heimdall to 0.17.17 or later.

## Is CVE-2026-57210 being exploited?

There is no known exploitation of CVE-2026-57210 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-57210 and fix it if it is affected.

What it is: CVE-2026-57210 is a high-severity vulnerability in dadrus heimdall, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-57210 in the wild and no public exploit code.

Affected packages and fixed versions:
- https://github.com/dadrus/heimdall (Go): affected all versions; fixed in 0.17.17
- https://github.com/dadrus/heimdall (Go): affected all versions; fixed in 0.17.17
- github.com/dadrus/heimdall (Go): affected all versions; fixed in 0.17.17

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-2026-57210/ (Markdown: https://insights.sbomify.com/CVE-2026-57210/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-57210
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-57210
- OSV: https://osv.dev/vulnerability/CVE-2026-57210

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-57210/
Summaries are generated and may contain mistakes; the official description above is the record.