CVE-2026-100353: kin-openapi Incomplete Fix For GHSA-p6wj-qrr4-pgh5: Three Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vrcc-3ch7-hppw",
  "modified" : "2026-10-15T20:20:47Z",
  "published" : "2026-10-15T20:20:47Z",
  "aliases" : [ "CVE-2026-100353" ],
  "summary" : "kin-openapi: Incomplete Fix for GHSA-p6wj-qrr4-pgh5: Three Unpatched nil-Items Panic Paths in openapi3filter",
  "details" : "## Summary\n\nThe fix for GHSA-p6wj-qrr4-pgh5 addressed a nil-pointer dereference that occurs when an OpenAPI 3.1 array schema omits the `items` keyword (which is legal under JSON Schema 2020-12). That fix patched three decoder paths: the standalone `parseArray` function, the top-level array check in `UrlencodedBodyDecoder`, and `MultipartBodyDecoder`.\n\nThree additional crash paths were missed. All of them reach the unguarded `urlValuesDecoder.parseArray` method (`openapi3filter/req_resp_decoder.go:576`) or the unguarded array branch in `buildResObj` (line 1015):\n\n1. **Query parameters** with `type: array` and no `items`.\n2. **deepObject** query parameters containing an array property with no `items`.\n3. **URL-encoded request bodies** where the array lives inside an `allOf` / `anyOf` / `oneOf` sub-schema. This path bypasses the guard added by the GHSA-p6wj-qrr4-pgh5 fix, because that guard only inspects top-level properties.\n\nEach path is triggerable by an unauthenticated client and produces a deterministic nil-pointer panic during request validation.\n\n## Details\n### Root Cause\n\nThe three paths patched for GHSA-p6wj-qrr4-pgh5 each received a nil-`items` guard:\n\n```go\n// standalone parseArray (line 1143) -- GUARDED\nfunc parseArray(raw []string, schemaRef *openapi3.SchemaRef) ([]any, error) {\n\tif schemaRef.Value.Items == nil || schemaRef.Value.Items.Value == nil { ... }\n\n// UrlencodedBodyDecoder top-level property loop (line 1441) -- GUARDED\nif propSchema.Value.Items == nil || propSchema.Value.Items.Value == nil { ... }\n\n// MultipartBodyDecoder (line 1587) -- GUARDED\nif valueSchema.Value.Items == nil { ... }\n```\n\nBut `urlValuesDecoder.parseArray` (line 576), which handles query-parameter and urlencoded-body array decoding, has **no** such guard:\n\n```go\nfunc (d *urlValuesDecoder) parseArray(raw []string, schemaRef *openapi3.SchemaRef) ([]any, error) {\n\tvar value []any\n\tfor i, v := range raw {\n\t\titem, err := d.parseValue(v, schemaRef.Value.Items) // Items is nil -> panic in parseValue\n```\n\n`parseValue` immediately dereferences the schema it is handed:\n\n```go\nfunc (d *urlValuesDecoder) parseValue(v string, schema *openapi3.SchemaRef) (any, error) {\n\tif len(schema.Value.AllOf) > 0 {   // schema == nil here -> nil pointer dereference\n```\n\nFor the deepObject path, `buildResObj` (line 1015) has the same gap. Its array branch recurses with `schema.Value.Items` (line 1028), which can be nil, and the recursive call dereferences it at line 1015:\n\n```go\ncase schema.Value.Type.Is(\"array\"):\n\t// ...\n\tfor i := range arr {\n\t\tr, err := buildResObj(params, mapKeys, strconv.Itoa(i), schema.Value.Items) // nil Items\n```\n\nFor the allOf body path, `UrlencodedBodyDecoder` validates only top-level `schema.Value.Properties` (line 1429-1449). But `decodeSchemaConstructs` (line 1474) recursively walks `AllOf` / `AnyOf` / `OneOf` sub-schemas and calls `decodeProperty` on their properties, which never pass through the top-level guard and reach `urlValuesDecoder.parseArray`.\n\n## Proof of Concept\n\n### Environment\n\n- kin-openapi v0.144.0 (cloned at tag `v0.144.0`, commit `f0407d5`)\n- Go 1.26.7\n- Each PoC calls `doc.Validate()` first to prove the spec is legal, then drives `openapi3filter.ValidateRequest` directly\n\n### Path 1: Query parameter array without items\n\nSpec (query param `ids` is `type: array`, no `items`), request `GET /test?ids=1&ids=2`:\n\n```\nValidate() ACCEPTED the spec (type: array with no items is legal under OAS 3.1)\nCalling ValidateRequest directly (no net/http recover)...\npanic: runtime error: invalid memory address or nil pointer dereference\n[signal 0xc0000005 code=0x0 addr=0x20 ...]\ngithub.com/getkin/kin-openapi/openapi3filter.(*urlValuesDecoder).parseValue(...)\n\treq_resp_decoder.go:605\ngithub.com/getkin/kin-openapi/openapi3filter.(*urlValuesDecoder).parseArray(...)\n\treq_resp_decoder.go:580\ngithub.com/getkin/kin-openapi/openapi3filter.(*urlValuesDecoder).DecodeArray(...)\n\treq_resp_decoder.go:569\n...\ngithub.com/getkin/kin-openapi/openapi3filter.ValidateRequest(...)\n\tvalidate_request.go:83\nexit status 2\n```\n\n### Path 2: deepObject nested array without items\n\nSpec (deepObject param `filter` with array property `tags`, no `items`), request `GET /test?filter[tags][0]=a`:\n\n```\nValidate() ACCEPTED the spec\nCalling ValidateRequest directly...\npanic: runtime error: invalid memory address or nil pointer dereference\ngithub.com/getkin/kin-openapi/openapi3filter.buildResObj(...)\n\treq_resp_decoder.go:1012\ngithub.com/getkin/kin-openapi/openapi3filter.buildResObj(...)   <- recursive call with nil Items\n\treq_resp_decoder.go:1028\ngithub.com/getkin/kin-openapi/openapi3filter.makeObject(...)\n\treq_resp_decoder.go:947\n...\nexit status 2\n```\n\n### Path 3: URL-encoded body with array inside allOf (bypasses the existing fix)\n\nSpec (urlencoded body, `allOf` sub-schema with array property `tags`, no `items`), request `POST /submit` body `tags=a&tags=b`:\n\n```\nValidate() ACCEPTED the spec\nCalling ValidateRequest directly...\npanic: runtime error: invalid memory address or nil pointer dereference\ngithub.com/getkin/kin-openapi/openapi3filter.(*urlValuesDecoder).parseValue(...)\n\treq_resp_decoder.go:605\ngithub.com/getkin/kin-openapi/openapi3filter.(*urlValuesDecoder).parseArray(...)\n\treq_resp_decoder.go:580\ngithub.com/getkin/kin-openapi/openapi3filter.(*urlValuesDecoder).DecodeArray(...)\n\treq_resp_decoder.go:569\n...\ngithub.com/getkin/kin-openapi/openapi3filter.decodeProperty(...)   <- reached via decodeSchemaConstructs (allOf walker)\n\treq_resp_decoder.go:1519\nexit status 2\n```\n\nThe `decodeProperty` frame confirms the array was reached by walking the `allOf` sub-schema, bypassing the top-level guard that the GHSA-p6wj-qrr4-pgh5 fix added.\n\n### Fix verification\n\nAdding a single nil-`items` guard to `urlValuesDecoder.parseArray` (plus one to the `buildResObj` array branch) turns all three panics into clean validation errors:\n\n```\npoc1: Returned normally, err = parameter \"ids\" in query has an error: array items schema is required for decoding\npoc2: Returned normally, err = parameter \"filter\" in query has an error: path tags: array items schema is required\npoc3: Returned normally, err = <nil>   (no panic; the allOf property is skipped by the decoder)\n```\n\nThis confirms `urlValuesDecoder.parseArray` is the shared root cause for Paths 1 and 3, and `buildResObj` for Path 2.\n\n## Impact\n\nAn unauthenticated client can trigger a deterministic nil-pointer panic in request validation with a single crafted request, against any application that validates OAS 3.1 requests with `openapi3filter` where a spec declares an array without `items`.\n\nThe severity depends on the host:\n\n| Deployment | Behavior | Availability impact |\n|------------|----------|---------------------|\n| Standard `net/http` server (validation runs in the handler goroutine) | `net/http` recovers the panic per-connection; the connection is dropped and the process survives | Per-request denial of service (A:L) |\n| Non-`net/http` hosts (e.g. fasthttp/connect adapters) or validation performed in an application-spawned goroutine | The panic is not recovered; the process crashes | Full-process denial of service (A:H) |\n\nThis was verified in both configurations: under a live `net/http` server the process survived (the panic was logged as `http: panic serving ...` and the process exited 0 at end of test), while the direct-call PoCs above crashed the process with `exit status 2`.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/getkin/kin-openapi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.136.0"
      }, {
        "fixed" : "0.149.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/getkin/kin-openapi/security/advisories/GHSA-vrcc-3ch7-hppw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-100353"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/getkin/kin-openapi/commit/9814d1f2b212f3508bf52296aa9e248b2122a5a9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/getkin/kin-openapi"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/getkin/kin-openapi/releases/tag/v0.149.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-476" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-15T20:20:47Z",
    "nvd_published_at" : "2026-10-15T17:17:07Z"
  }
}