Description

Budibase: Webhook schema endpoint authorization bypass allows unauthenticated mutation of webhook and automation schema The webhook schema-building endpoint is registered under builderRoutes, but the generic authorization middleware skips authorization for all paths matching /api/webhooks/schema. As a result, an unauthenticated caller can update the body schema for a known webhook and mutate the corresponding automation trigger output schema.

Details

The route appears to be builder-only:

packages/server/src/api/routes/webhook.ts:5-9

5:builderRoutes
6:  .get("/api/webhooks", controller.fetch)
7:  .put("/api/webhooks", webhookValidator(), controller.save)
8:  .delete("/api/webhooks/:id/:rev", controller.destroy)
9:  .post("/api/webhooks/schema/:instance/:id", controller.buildSchema)

However, webhook endpoint detection explicitly includes schema:

packages/server/src/middleware/utils.ts:3-9

3:const WEBHOOK_ENDPOINTS = new RegExp(
4:  "^/api/webhooks/(trigger|schema|discord|ms-teams|slack)(/|$)"
5:)
6:
7:export function isWebhookEndpoint(ctx: UserCtx): boolean {
8:  const path = ctx.path || ctx.request.url.split("?")[0]
9:  return WEBHOOK_ENDPOINTS.test(path)

The authorization middleware bypasses all webhook endpoints before checking ctx.user or permissions:

packages/server/src/middleware/authorized.ts:90-99

90:  ) =>
91:  async (ctx: UserCtx, next: any) => {
92:    // webhooks don't need authentication, each webhook unique
93:    // also internal requests (between services) don't need authorized
94:    if (isWebhookEndpoint(ctx) || ctx.internal) {
95:      return next()
96:    }
97:...
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The bypassed controller writes attacker-derived schema data to the webhook and automation trigger outputs:

packages/server/src/api/controllers/webhook.ts:56-83

56:export async function buildSchema(
57:  ctx: Ctx<BuildWebhookSchemaRequest, BuildWebhookSchemaResponse>
58:) {
59:  await context.doInWorkspaceContext(ctx.params.instance, async () => {
60:    const db = context.getWorkspaceDB()
61:    const webhook = await db.get<Webhook>(ctx.params.id)
62:    webhook.bodySchema = toJsonSchema(ctx.request.body)
63:    // update the automation outputs...
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The route grouping suggests builder authorization was intended, but the global webhook bypass removes it.

PoC

Non-destructive validation approach:

Create a webhook-backed automation as a builder.

Record the workspace ID and webhook ID.

Log out or send no auth headers.

Send:

POST /api/webhooks/schema/<workspaceId>/<webhookId> HTTP/1.1
content-type: application/json

{"unauth_schema_probe":"test"}

Fetch the webhook as a builder and observe that bodySchema has changed.

For automation-backed webhooks, inspect the automation trigger schema outputs and observe that properties were reset/updated.

Impact

An unauthenticated attacker can modify webhook schema metadata and automation trigger output schema for known webhook IDs. This can corrupt builder-visible automation definitions, alter downstream binding behavior, and disrupt webhook-backed automation workflows.

Mitigation

Aliases

References