go-chi chi 0.9.0 before 5.3.0 IP Spoofing via X-Forwarded-For

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

go-chi/chi versions 0.9.0 before 5.3.0 contains an IP spoofing vulnerability in the RealIP middleware, which resolves the request source IP (Request.RemoteAddr) using the first IP in the X-Forwarded-For header without validating trusted proxies. A malicious client can prepend a forged IP as the first value of the X-Forwarded-For header to spoof the request source IP, potentially bypassing access controls or falsifying request logs.

Source published

14 Aug 2026 11:35:28 UTC

Source modified

8 Oct 2026 15:24:32 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

go-chi/chi versions 0.9.0 before 5.3.0 contains an IP spoofing vulnerability in the RealIP middleware, which resolves the request source IP (Request.RemoteAddr) using the first IP in the X-Forwarded-For header without validating trusted proxies. A malicious client can prepend a forged IP as the first value of the X-Forwarded-For header to spoof the request source IP, potentially bypassing access controls or falsifying request logs.

Source published

Aug 14, 2026, 11:35:28 AM (timezone not stated)

Source modified

Oct 8, 2026, 3:24:32 PM (timezone not stated)

Observed here

9 Nov 2026 15:08:45 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD 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

go-chi/chi versions 0.9.0 before 5.3.0 contains an IP spoofing vulnerability in the RealIP middleware, which resolves the request source IP (Request.RemoteAddr) using the first IP in the X-Forwarded-For header without validating trusted proxies. A malicious client can prepend a forged IP as the first value of the X-Forwarded-For header to spoof the request source IP, potentially bypassing access controls or falsifying request logs.

Source published

14 Aug 2026 12:16:44 UTC

Source modified

8 Oct 2026 16:17:35 UTC

Observed here

25 Oct 2026 15:19:03 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

### Summary The vulnerability allows the `Request.RemoteAddr` to be spoofed when determining the request source IP via the `X-Forwarded-For` header. This could result in misidentification of the request source and potentially compromise access control and logging integrity. ### Details Currently, the `RealIP()` implementation splits the `X-Forwarded-For` header by `,` and uses the first IP. https://github.com/go-chi/chi/blob/v5.1.0/middleware/realip.go#L50-L54 However, relying on the first IP in the `X-Forwarded-For` header is insecure because it can be manipulated by attackers to falsify the source IP. Malicious Case: 1. A malicious client sends a request with a forged IP in the X-Forwarded-For header: `X-Forwarded-For: <forged-ip>` 2. The proxy appends the actual client’s IP and forwards the request: `X-Forwarded-For: <forged-ip>,<client-ip>` 3. If the server always uses the first IP, it becomes vulnerable to IP spoofing. Ideally, the implementation should verify IPs starting from the end of the `X-Forwarded-For` header value, skipping trusted IPs within the system, and using the first untrusted IP as the actual client IP. For example, the `labstack/echo` web framework processes the `X-Forwarded-For` header by checking IPs from the end, skipping trusted IPs, and using the first untrusted IP as the client's ip. https://github.com/labstack/echo/blob/v4.13.2/ip.go#L261-L273 ### PoC #### 1. Run the Go application with the following code: ```go package main import ( "fmt" "log" "net/http" "github.com/go-chi/chi/v5/middleware" ) func main() { // Set handler to print the remote address handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { fmt.Fprintln( w, fmt.Sprintf("remote addr: %s (want 192.0.2.1)", r.RemoteAddr), ) }) // Use RealIP middleware log.Fatal(http.ListenAndServe(":8080", middleware.RealIP(handler))) } ``` #### 2. Send a request to the server using curl with a manipulated X-Forwarded-For header: ``` $ curl localhost:8080 -H 'X-Forwarded-For: 192.0.2.2, 192.0.2.1' remote addr: 192.0.2.2 (want 192.0.2.1) ``` ### Impact This vulnerability can lead to a request source IP spoofing issue, which may allow attackers to bypass access controls or falsify request logs. It primarily affects systems that rely on X-Forwarded-For to determine the actual client IP, particularly in scenarios where intermediary proxies or load balancers are involved.

Source published

25 Jun 2026 18:18:56 UTC

Source modified

10 Sep 2026 03:50:49 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P

Publisher rating · HIGH

Chi Middleware vulnerable to IP spoofing via X-Forwarded-For header in github.com/go-chi/chi

Source published

24 Jul 2026 18:35:55 UTC

Source modified

15 Aug 2026 05:19:13 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.