vulnerability / NVI-00016033 / Revision 2
Heimdall: Forwarded Header Injection via Unsanitized Host Header in Proxy Mode
GitHub lists this reviewed advisory for github.com/dadrus/heimdall. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
0.488%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.42157. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
github.com/dadrus/heimdall
source listed<= 0.17.16
### Summary 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. ### Vulnerable Code **File: `proxy/request_context.go` (line 201)** ```go entry := "for=" + clientIP + ";host=" + in.Host + ";proto=" + proto ``` Go's `net/http` allows commas and semicolons in Host header values. No sanitization is applied before string concatenation. ### PoC ```bash # Inject a spoofed IP into the Forwarded header curl -s -H "Host: evil.com,for=127.0.0.1" \ "http://TARGET:PORT/protected-resource" ``` This produces the following `Forwarded` header sent to the upstream service: ``` Forwarded: for=1.2.3.4;host=evil.com, for=127.0.0.1;proto=http ``` Upstream services that parse the `Forwarded` header according to RFC 7239 will see two entries. If the service trusts the last or any `for=` value, the attacker successfully spoofs `127.0.0.1` as the client IP. `
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-4jgr-pg2m-m988 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-57209 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.