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Medium, CVSS 6.9amended

chi Has an IP Spoofing Vulnerability in middleware.RealIP

CVE-2026-72815GHSA-3fxj-6jh8-hvhx

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/go-chi/chi/v5 5.3.0; github.com/go-chi/chi/v5/middleware 5.3.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-72815: 0.50% estimated exploitation activity in the next 30 days; percentile 42.51 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary The `RealIP` middleware in `go-chi/chi` is vulnerable to IP spoofing because it blindly trusts the first (leftmost) element of the `X-Forwarded-For` HTTP header. This allows a remote attacker to bypass IP-based access control lists (ACLs) and rate-limiting mechanisms by providing a spoofed IP address in the header.

Details In `middleware/realip.go`, the `realIP` function parses the `X-Forwarded-For` header and extracts the first comma-separated value: ```go func realIP(r *http.Request) string { // ... } else if xff := r.Header.Get(xForwardedFor); xff != "" { ip, _, _ = strings.Cut(xff, ",") } // ... } ``` Standard practice for `X-Forwarded-For` is that each proxy appends the client's IP to the end of the list. However, since the client can also provide this header, the leftmost values are untrusted. A client can send a header like `X-Forwarded-For: , `, and `go-chi/chi` will treat ` ` as the source of the request.

Proof of Concept (PoC) The following code…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from osv record GHSA-3fxj-6jh8-hvhx

  2. Revision 2 · amended ·

    Amended from ghsa record GHSA-3fxj-6jh8-hvhx

  3. Revision 1 · created ·

    Published from ghsa record GHSA-3fxj-6jh8-hvhx

Agent brief

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# Patch Next advisory brief: CVE-2026-72815

Advisory: chi Has an IP Spoofing Vulnerability in `middleware.RealIP`
IDs: CVE-2026-72815, GHSA-3fxj-6jh8-hvhx
Record: https://patchnext.com/advisories/ghsa-3fxj-6jh8-hvhx (revision 3, source checked 4 Nov 2026, 06:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/go-chi/chi/v5 5.3.0; github.com/go-chi/chi/v5/middleware 5.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/go-chi/chi/v5: affected >= 5.2.1, < 5.3.0; fixed in 5.3.0
- Go github.com/go-chi/chi/v5/middleware: affected >= 5.2.1, < 5.3.0; fixed in 5.3.0

## Suggested inspection (read-only)
- Go github.com/go-chi/chi/v5: check the installed version with your package manager.
- Go github.com/go-chi/chi/v5/middleware: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/go-chi/chi/v5, github.com/go-chi/chi/v5/middleware.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-3fxj-6jh8-hvhx (GitHub-reviewed advisory GHSA-3fxj-6jh8-hvhx lists affected ranges: Go github.com/go-chi/chi/v5/middleware >=5.2.1 <5.3.0)
- Verified: https://github.com/advisories/GHSA-3fxj-6jh8-hvhx (GitHub-reviewed advisory GHSA-3fxj-6jh8-hvhx lists affected ranges: Go github.com/go-chi/chi/v5/middleware >=5.2.1 =5.2.1 <5.3.0)
- Verified: https://osv.dev/vulnerability/GHSA-3fxj-6jh8-hvhx (OSV record GHSA-3fxj-6jh8-hvhx lists affected ranges: Go github.com/go-chi/chi/v5/middleware >=5.2.1 =5.2.1 <5.3.0 (fixed))

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