kin-openapi is a Go project for handling OpenAPI files. From 0.10.0 until 0.141.0, openapi3filter.convertParseError in openapi3filter/validation_error_encoder.go dereferences e.Parameter.In without checking whether e.Parameter is nil. A malformed non-string scalar field in a multipart/form-data request body produces a nested ParseError with a nil RequestError.Parameter, and applications that render the validation error through openapi3filter.ConvertErrors or ValidationErrorEncoder panic. An unauthenticated client can repeatedly send such requests to deny service when the application lacks a recovery boundary. JSON request bodies and applications that do not use these error-rendering helpers are not affected. This issue is fixed in version 0.141.0.

Affected: Go: github.com/getkin/kin-openapi

### Summary

A nil-pointer dereference in `openapi3filter.ConvertErrors` lets any unauthenticated client crash a server with a single HTTP request. When an application validates a `multipart/form-data` request body and renders the resulting validation error through the library-provided `ValidationErrorEncoder` / `ConvertErrors` helpers, a malformed scalar form field (e.g. a non-numeric value for an `integer` property) produces an error shape that `convertParseError` dereferences without a nil check. The handler goroutine panics, causing a denial of service. `application/json` request bodies are **not** affected — the bug is specific to `multipart/form-data`.

### Details

The panic is in `convertParseError`, at [`openapi3filter/validation_error_encoder.go:119-120`](https://github.com/getkin/kin-openapi/blob/master/openapi3filter/validation_error_encoder.go#L119) (still present on `master` at the time of writing):

```go } else if innerErr.RootCause() != nil { if rootErr, ok := innerErr.Cause.(*ParseError); ok && rootErr.Kind == KindInvalidFormat && e.Parameter.In == "query" { // ❌ e.Parameter may be nil → panic ```

The comparison `e.Parameter.In == "query"` assumes `e.Parameter` is non-nil. It is reached whenever **both** of the following hold:

1. **`e.Parameter == nil`.** A `*RequestError` carries *either* `Parameter` (parameter errors) *or* `RequestBody` (body errors), never both. `ValidateRequestBody` builds body errors with only `RequestBody` set, leaving…

encoding/asn1: golang: Go encoding/asn1: Denial of Service via excessive recursion in Unmarshal github.com/open-telemetry/opentelemetry-go: go.opentelemetry.io/otel/baggage: go.opentelemetry.io/otel/propagation: OpenTelemetry-Go: Denial of Service via oversized baggage headers golang.org/x/text: golang.org/x/text: Denial of Service via invalid UTF-8 input net/http: golang: Go net/http: Unencrypted HTTP/2 connections vulnerable to Denial of Service html/template: golang: Go html/template: Cross-Site Scripting via pathological input encoding/xml: golang: Go: Denial of Service via XML decoding recursion depth issue net/url: golang: golang net/url: Denial of Service from quadratic complexity in path resolution crypto/tls: golang: Golang crypto/tls: Denial of Service via indefinite KeyUpdate messages github.com/getkin/kin-openapi: kin-openapi: kin-openapi: ValidationHandler.Load() Fail-Open Authentication Bypass via NoopAuthenticationFunc Default github.com/getkin/kin-openapi: kin-openapi: Denial of Service via unauthenticated nil-pointer dereference github.com/getkin/kin-openapi: kin-openapi: Denial of Service via malformed multipart/form-data body github.com/getkin/kin-openapi: kin-openapi: Denial of Service via uncontrolled resource consumption in deepObject query parameter decoding

Affected: Ubuntu:22.04:LTS: golang-github-getkin-kin-openapi, Ubuntu:24.04:LTS: golang-github-getkin-kin-openapi, Ubuntu:26.04:LTS: golang-github-getkin-kin-openapi

kin-openapi is a Go project for handling OpenAPI files. From 0.10.0 until 0.141.0, openapi3filter.convertParseError in openapi3filter/validation_error_encoder.go dereferences e.Parameter.In without checking whether e.Parameter is nil. A malformed non-string scalar field in a multipart/form-data request body produces a nested ParseError with a nil RequestError.Parameter, and applications that render the validation error through openapi3filter.ConvertErrors or ValidationErrorEncoder panic. An unauthenticated client can repeatedly send such requests to deny service when the application lacks a recovery boundary. JSON request bodies and applications that do not use these error-rendering helpers are not affected. This issue is fixed in version 0.141.0.