kin-openapi openapi3filter: nil-pointer panic in ValidateResponse on a response header declared with content

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

kin-openapi is a Go project for handling OpenAPI files. Prior to 0.146.0, openapi3filter.ValidateResponse passes a nil response header schema to decodeValue when an OpenAPI document declares the header with content instead of schema. The document passes validation, but every response validation for the affected operation dereferences the nil schema and panics even when the response does not contain the declared header. Applications that ingest an untrusted specification can expose this as remote availability impact, while applications using only trusted local specifications still crash when the affected operation is exercised. This issue is fixed in version 0.146.0.

Source published

15 Oct 2026 15:50:37 UTC

Source modified

16 Oct 2026 17:13:28 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

kin-openapi is a Go project for handling OpenAPI files. Prior to 0.146.0, openapi3filter.ValidateResponse passes a nil response header schema to decodeValue when an OpenAPI document declares the header with content instead of schema. The document passes validation, but every response validation for the affected operation dereferences the nil schema and panics even when the response does not contain the declared header. Applications that ingest an untrusted specification can expose this as remote availability impact, while applications using only trusted local specifications still crash when the affected operation is exercised. This issue is fixed in version 0.146.0.

Source published

Oct 15, 2026, 3:50:37 PM (timezone not stated)

Source modified

Oct 16, 2026, 5:13:28 PM (timezone not stated)

Observed here

9 Nov 2026 04:15:08 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

kin-openapi is a Go project for handling OpenAPI files. Prior to 0.146.0, openapi3filter.ValidateResponse passes a nil response header schema to decodeValue when an OpenAPI document declares the header with content instead of schema. The document passes validation, but every response validation for the affected operation dereferences the nil schema and panics even when the response does not contain the declared header. Applications that ingest an untrusted specification can expose this as remote availability impact, while applications using only trusted local specifications still crash when the affected operation is exercised. This issue is fixed in version 0.146.0.

Source published

15 Oct 2026 16:17:30 UTC

Source modified

16 Oct 2026 18:17:10 UTC

Observed here

25 Oct 2026 04:17:26 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

## Summary `ValidateResponse` panics on a nil pointer when a spec declares a response header with `content` instead of `schema`. `doc.Validate()` accepts that document, so the crash comes from a spec the library just called valid. Same class as GHSA-jpcw-4wr7-c3vq, which covered the request-parameter case in v0.144.0; this is the response-header path. Affects `github.com/getkin/kin-openapi` `<= v0.145.0`. Reproduced on master `947498e5a6bd`, Go 1.26. ## Details A `content`-typed response header has `headerRef.Value.Schema == nil`. `validate_response.go:181` passes it straight through: ```go if decodedValue, found, err = decodeValue(dec, headerName, sm, headerRef.Value.Schema, headerRef.Value.Required); err != nil { ``` and `req_resp_decoder.go:273` is where it lands: ```go if len(schema.Value.AllOf) > 0 { ``` Two things I checked rather than assumed. The response does not need to carry the header; declaring it is enough, and then every call for that operation panics. And the body path is fine, `:114` returns early on a nil schema, so this is headers only. The PoC keeps the body case as a control. ## PoC Drop into `openapi3filter/` and run: ``` go test ./openapi3filter/ -run NilSchema -v ``` ```go package openapi3filter_test import ( "context" "io" "net/http" "net/http/httptest" "strings" "testing" "github.com/getkin/kin-openapi/openapi3" "github.com/getkin/kin-openapi/openapi3filter" "github.com/getkin/kin-openapi/routers" ) const specBody = ` openapi: 3.0.3 info: {title: poc, version: "1.0.0"} paths: /x: get: responses: "200": description: ok content: application/json: {} ` const specHeader = ` openapi: 3.0.3 info: {title: poc, version: "1.0.0"} paths: /x: get: responses: "200": description: ok headers: X-Thing: content: application/json: {} ` func validatedInput(t *testing.T, spec string, hdr http.Header) *openapi3filter.ResponseValidationInput { t.Helper() doc, err := openapi3.NewLoader().LoadFromData([]byte(spec)) if err != nil { t.Fatalf("load: %v", err) } if err := doc.Validate(context.Background()); err != nil { t.Fatalf("doc.Validate rejected the spec, so this repro proves nothing: %v", err) } op := doc.Paths.Find("/x").Get req := httptest.NewRequest(http.MethodGet, "/x", nil) return &openapi3filter.ResponseValidationInput{ RequestValidationInput: &openapi3filter.RequestValidationInput{ Request: req, Route: &routers.Route{Spec: doc, Operation: op, Method: http.MethodGet, Path: "/x"}, }, Status: 200, Header: hdr, Body: io.NopCloser(strings.NewReader(`{}`)), } } // Control: body path returns early on a nil schema. func TestControl_ResponseBodyNilSchema(t *testing.T) { in := validatedInput(t, specBody, http.Header{"Content-Type": {"application/json"}}) defer func() { if r := recover(); r != nil { t.Errorf("body path panicked, expected clean return: %v", r) } }() if err := openapi3filter.ValidateResponse(context.Background(), in); err != nil { t.Errorf("body path returned %v, expected nil", err) } } // The response does not carry X-Thing. Declaring the header is enough. func TestResponseHeaderNilSchema(t *testing.T) { in := validatedInput(t, specHeader, http.Header{"Content-Type": {"application/json"}}) if err := openapi3filter.ValidateResponse(context.Background(), in); err != nil { t.Fatalf("no panic; got err = %v (already fixed?)", err) } } ``` Output: ``` === RUN TestControl_ResponseBodyNilSchema --- PASS: TestControl_ResponseBodyNilSchema (0.00s) === RUN TestResponseHeaderNilSchema --- FAIL: TestResponseHeaderNilSchema (0.00s) panic: runtime error: invalid memory address or nil pointer dereference [recovered, repanicked] [signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x7f6d2a] github.com/getkin/kin-openapi/openapi3filter.decodeValue(...) /src/openapi3filter/req_resp_decoder.go:273 +0x4a github.com/getkin/kin-openapi/openapi3filter.validateResponseHeader(...) /src/openapi3filter/validate_response.go:181 +0x146 github.com/getkin/kin-openapi/openapi3filter.ValidateResponse(...) /src/openapi3filter/validate_response.go:89 +0xafa ``` The `FAIL` is the point: control passes, the header case takes the binary down. Ran in a container against a fresh clone of master. I have not tried it against a live proxy. ## Impact A process crash instead of an error return. Declaring the header is enough, so it is every call on that operation rather than an occasional one. If the spec comes from somewhere else -- gateways, linters, anything ingesting specs it did not write -- that is a trust boundary, and it becomes remote availability. If it is your own spec, nothing attacker-controlled starts it, but any client reaching that route then crashes the process. It fires on every call, so normally you would see it the first time that route runs. A spec edited without exercising the route is the case where you would not. That is the difference from GHSA-jpcw, where the attacker supplied the trigger. I have left severity unset; the two cases do not score the same. On how common it is, I checked rather than guessed. Of roughly 1,500 OpenAPI 3.x specs on apis.guru, one declares content-typed response headers -- VTEX Catalog API -- and not in one corner of it: the shape repeats across its operations, so for that consumer this is not an edge case. The header names in it (`X-AspNet-Version`, `p3p`, a few malformed ones) look like a generator emitting `content` where it could not infer a schema, and apis.guru only indexes public specs. There is no content-typed response header in this repo's testdata either. ## Workarounds Use `schema` on the response header, or skip `ValidateResponse` for those operations. `ExcludeResponseBody` will not do it -- headers are validated before that check. ## Suggested fix Nil-guard at the top of `decodeValue`: ```go if schema == nil { return nil, false, nil } ``` Returning nil leaves a `content`-typed header unvalidated rather than erroring, so it trades the crash for a silent gap. An error return kills the panic just as well if you would rather it surfaced.

Source published

16 Oct 2026 19:58:46 UTC

Source modified

5 Nov 2026 23:25:38 UTC

Observed here

5 Nov 2026 23:38:32 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Publisher rating · HIGH

kin-openapi openapi3filter: nil-pointer panic in ValidateResponse on a response header declared with content in github.com/getkin/kin-openapi

Source published

5 Nov 2026 22:53:53 UTC

Source modified

5 Nov 2026 23:15:12 UTC

Observed here

5 Nov 2026 23:38:32 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.