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fix(mcp-gateway): tighten auxiliary header validation #7977

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fix(mcp-gateway): tighten auxiliary header validation #7977

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25 changes: 25 additions & 0 deletions packages/mcp-gateway/src/headers.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,8 @@ const hopByHopHeaders = new Set([
'upgrade',
]);

const framingHeader = 'content-length';

const headerNamePattern = /^[A-Za-z0-9!#$%&'*+.^_`|~-]+$/;

const blockedExactHeaders = new Set([
Expand Down Expand Up @@ -102,6 +104,13 @@ const staticHeadersSchema = z.record(z.string(), headerValueSchema).superRefine(
path: [name],
});
}
if (normalized === framingHeader) {
ctx.addIssue({
code: z.ZodIssueCode.custom,
message: 'Static header cannot be a framing header',
path: [name],
});
}
}
});

Expand All @@ -124,6 +133,20 @@ const auxiliaryHeadersSchema = z
path: [name],
});
}
if (isTransportIdentityHeader(normalized)) {
ctx.addIssue({
code: z.ZodIssueCode.custom,
message: 'Auxiliary header cannot be transport identity metadata',
path: [name],
});
}
if (normalized === framingHeader) {
ctx.addIssue({
code: z.ZodIssueCode.custom,
message: 'Auxiliary header cannot be a framing header',
path: [name],
});
}
}
});

Expand Down Expand Up @@ -164,6 +187,8 @@ export function buildUpstreamHeaders(params: {
if (
hopByHopHeaders.has(normalized) ||
isCredentialLikeHeader(normalized) ||
isTransportIdentityHeader(normalized) ||
normalized === framingHeader ||
blockedStaticNames.has(normalized)
)
continue;
Expand Down
48 changes: 48 additions & 0 deletions packages/mcp-gateway/src/index.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ import {
buildScopedConnectRootPath,
buildUpstreamHeaders,
parseScopedConnectPath,
parseAuxiliaryHeaders,
parseStaticHeaders,
isPublicIp,
ProviderGrantBundleSchema,
Expand Down Expand Up @@ -118,6 +119,50 @@ describe('provider grant schema', () => {
});
});

describe('auxiliary headers', () => {
test('rejects transport identity and framing headers', () => {
expect(() => parseAuxiliaryHeaders({ Host: 'example.com' })).toThrow(
'Auxiliary header cannot be transport identity metadata'
);
expect(() => parseAuxiliaryHeaders({ Forwarded: 'for=192.0.2.1' })).toThrow(
'Auxiliary header cannot be transport identity metadata'
);
expect(() => parseAuxiliaryHeaders({ 'X-Forwarded-For': '192.0.2.1' })).toThrow(
'Auxiliary header cannot be transport identity metadata'
);
expect(() => parseAuxiliaryHeaders({ 'X-Forwarded-Host': 'example.com' })).toThrow(
'Auxiliary header cannot be transport identity metadata'
);
expect(() => parseAuxiliaryHeaders({ 'CF-Connecting-IP': '192.0.2.1' })).toThrow(
'Auxiliary header cannot be transport identity metadata'
);
expect(() => parseAuxiliaryHeaders({ 'Content-Length': '10' })).toThrow(
'Auxiliary header cannot be a framing header'
);
expect(parseAuxiliaryHeaders({ 'X-Request-Id': 'request-1' })).toEqual({
'X-Request-Id': 'request-1',
});
});

test('buildUpstreamHeaders drops transport identity and framing auxiliary headers', () => {
const headers = buildUpstreamHeaders({
source: new Headers({ Accept: 'application/json' }),
auxiliaryHeaders: [
['Host', 'attacker.example'],
['X-Forwarded-For', '192.0.2.1'],
['Content-Length', '10'],
['X-Request-Id', 'request-1'],
],
});

expect(headers.get('host')).toBeNull();
expect(headers.get('x-forwarded-for')).toBeNull();
expect(headers.get('content-length')).toBeNull();
expect(headers.get('x-request-id')).toBe('request-1');
expect(headers.get('accept')).toBe('application/json');
});
});

describe('static headers', () => {
test('allows authorization but rejects transport identity headers', () => {
expect(parseStaticHeaders({ Authorization: 'Bearer test' })).toEqual({
Expand All @@ -132,6 +177,9 @@ describe('static headers', () => {
expect(() => parseStaticHeaders({ 'CF-Connecting-IP': '203.0.113.1' })).toThrow(
'Static header cannot be transport identity metadata'
);
expect(() => parseStaticHeaders({ 'Content-Length': '10' })).toThrow(
'Static header cannot be a framing header'
);
expect(
parseStaticHeaders({
'CF-Access-Client-Id': 'client-id',
Expand Down