4.8 Medium

chi: Client IP spoofing in ClientIPFromXFF via X-Forwarded-For

CVE-2026-114437

Summary ClientIPFromXFF skips any X-Forwarded-For entry in a configured trusted CIDR but never verifies that the direct TCP peer in http.Request.RemoteAddr belongs to that CIDR. A client that can reach the Go server directly can therefore append a trusted-looking proxy address and choose the client IP returned by middleware.GetClientIP. The attack is remote and requires one unauthenticated HTTP request with no user interaction (AV:N/AC:L/PR:N/UI:N). It changes security decisions and exposes one protected handler within the same application (S:U/C:L/I:L); no availability loss was observed (A:N). Preconditions: The application uses ClientIPFromXFF and makes the origin server reachable by an anonymous client outside the configured trusted-proxy CIDRs. No victim interaction is required. 1. Send GET /admin directly to the origin with no X-Forwarded-For header. 2. Observe a 403 Forbidden response and an empty derived client IP. 3. Repeat the request with X-Forwarded-For: 10.0.0.7, 198.51.100.42. 4. Observe 200 OK and client-ip="10.0.0.7". Expected: the untrusted direct peer prevents the forwarding chain from being accepted. Details The vulnerable code is ClientIPFromXFF in…

Assessment

CVSS: 4.8 (v3.1)
Severity: Medium
EPSS: 0.00129% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published: 23 October 2026
Last updated: 23 October 2026
Affected: go · github.com/go-chi/chi/v5
Weakness: CWE-345

CVSS vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

At the source

GitHub Advisories

References

Community proofs of concept

No community proof of concept yet. If you have one for a published vulnerability and the right to share it, add it below — it will appear here once reviewed.

Submit a proof of concept

Only for publicly disclosed vulnerabilities, and only material from testing you were authorised to perform. This platform does not buy, sell, or broker exploits — see earning from vulnerability research for legitimate bounty programs. Submissions are reviewed before they appear. Text only; do not include live credentials, personal data, or anything targeting systems you are not permitted to test.

Title *

Proof of concept *

Write-up (optional)

Affected versions (optional)

Name or handle (optional)

References (optional, one URL per line)

Licence for your contribution *

Private contact (optional, never shown)

Before you submit * This vulnerability is already publicly disclosed (it has a published CVE). This material comes only from testing I was authorised to perform. I have the legal right to publish this content and am not breaching any agreement by doing so. It contains no live credentials, personal data, or anything targeting systems I am not authorised to test. I understand it will be reviewed before it appears publicly and may be rejected. I agree to the submission terms.

What is 6 + 8? *

Query this programmatically

Agents can read this through the MCP endpoint, or over HTTP:

curl https://cve.zerocrew.in/api/cve/CVE-2026-114437