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The vulnerability stems from a mismatch in request path representations between kin-openapi‘s validation middleware and downstream routers like `gorilla/mux` configured with UseEncodedPath(). Specifically, `openapi3filter.ValidationHandler.Middleware` uses a legacy router that selects OpenAPI operations based on decoded request paths (URL.Path), whereas the application’s downstream router selects handlers based on encoded representations (URL.RawPath). An unauthenticated remote attacker can supply a crafted encoded path such as `/public%2Fstatus` which the validation layer interprets as an intentionally public endpoint while the application router dispatches it to a protected parameterized operation (/{id}). Consequently, the security gate fails to invoke the authentication callback, allowing unauthorized requests to successfully reach protected handlers.
DailyCVE Form:
Platform: github.com/getkin/kin-openapi
Version: v0.144.0 to v0.146.0
Vulnerability : Path-Confusion Authentication Bypass
Severity: critical
date: 2026-08-18
Prediction: 2026-09-01
What Undercode Say
Analytics
The core security risk arises from discrepancy during request parsing where the verification layer evaluates decoded parameters (URL.Path) while downstream multiplexers handle raw encoded paths (URL.RawPath). Because validation and dispatching components disagree on the route identifier, access control logic checking public rules can be completely sidestepped for restricted parameterized routes.
Exploit: (Educational Purposes!)
package openapi3filter_test
import (
"net/http"
"net/http/httptest"
"testing"
"github.com/getkin/kin-openapi/openapi3filter"
)
func TestEncodedPathAuthorizationBypass(t testing.T) {
// PoC test case illustrating route confusion via encoded paths
req := httptest.NewRequest("GET", "/public%2Fstatus", nil)
rec := httptest.NewRecorder()
// Simulating mismatch between validation and routing layer
if req.URL.Path == "/public/status" {
t.Log("Validated as public path")
}
_ = rec
}
Protection: from this CVE
To secure applications against this vulnerability, developers must ensure consistency between the request representation evaluated by the validation framework and the downstream router. Upgrade `kin-openapi` to a patched version where router path semantics are unified, avoid mismatched configurations such as `gorilla/mux` with `UseEncodedPath()` unless explicitly normalized, and implement strict fail-closed request path validation filters.
Impact
An unauthenticated attacker can completely bypass security checks on protected endpoints that share overlapping structures with public literal paths. This results in unauthorized execution of sensitive backend handlers, potentially leading to confidentiality breaches or integrity violations depending on the permissions and capabilities of the reached operations.
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Sources:
Reported By: github.com
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