CVE-2026-100347 in kin-openapi
Summary
by MITRE • 10/15/2026
kin-openapi is a Go project for handling OpenAPI files. Prior to 0.145.0, openapi3filter.ValidationHandler uses the routers/legacy router, which passes an unsupported or non-canonical HTTP method for an existing static path to openapi3.PathItem.GetOperation. The default branch of GetOperation panics before authentication runs, so an unauthenticated remote client can repeatedly send methods such as PROPFIND or lowercase get to abort connections and generate stack-trace log growth. The specific panic requires an exact static path; a concrete path matched only by a templated route does not reach the same sink. This issue is fixed in version 0.145.0.
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Analysis
by VulDB Data Team • 10/15/2026
The kin-openapi library serves as a critical component for Go-based applications that need to parse, validate, and handle OpenAPI specifications. Within this ecosystem, the openapi3filter package provides validation handlers that enforce API contracts against incoming requests. A significant reliability flaw was identified in versions prior to 0.145.0, specifically within the ValidationHandler implementation which relies on a legacy routing mechanism. This architectural choice introduces a critical stability issue when handling HTTP methods that are not explicitly defined for specific static paths but match existing route patterns through non-canonical or unsupported method names.
The technical root cause lies in how the legacy router processes requests where the HTTP method does not have a corresponding operation definition in the OpenAPI specification for an exact, static path match. When such a request is received, the routing logic invokes openapi3.PathItem.GetOperation to retrieve the handler for that endpoint. However, because no valid operation exists for the specific combination of path and unsupported method, GetOperation returns nil or triggers an internal error condition rather than gracefully handling the mismatch. The ValidationHandler fails to check this return value before proceeding with authentication and validation logic, leading directly to a nil pointer dereference panic. This results in an immediate termination of the current request processing goroutine and generates extensive stack trace logs on the server side.
From a security operations perspective, this vulnerability constitutes a Denial of Service (DoS) vector that is particularly dangerous due to its unauthenticated nature. An attacker can exploit this flaw by sending repeated requests with unusual HTTP methods such as PROPFIND or lowercase variants like get instead of GET against endpoints that exist in the API specification but do not define those specific methods. Because the panic occurs before any authentication middleware runs, no credentials are required to trigger the service disruption. The continuous generation of stack traces can rapidly consume disk space and CPU resources, potentially rendering the application unavailable for legitimate users or causing cascading failures in dependent systems that rely on this API.
This issue is classified under CWE-476, which denotes a NULL Pointer Dereference vulnerability. In terms of offensive security frameworks, it aligns with MITRE ATT&CK technique T1499, specifically Endpoint Denial of Service via resource exhaustion through log flooding or application crashes. The attack vector is remote and requires no user interaction beyond the ability to send HTTP requests to the target endpoint. It highlights a common pitfall in API gateway implementations where strict adherence to specification-defined methods is not enforced at the routing layer before deeper processing occurs.
The vulnerability has been addressed in kin-openapi version 0.145.0 by improving the error handling within the ValidationHandler and ensuring that unsupported or non-canonical HTTP methods are rejected gracefully without causing a panic. Organizations using this library should upgrade to version 0.145.0 or later immediately to mitigate the risk of service disruption. Additionally, implementing rate limiting on API endpoints can provide an additional layer of defense against automated exploitation attempts while patching is applied. Monitoring for excessive stack trace logs in server outputs may also serve as an early detection mechanism for ongoing exploitation attempts in environments where upgrading has not yet been completed.