CVE-2026-48151: 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

ts 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

ts 3:const WEBHOOKENDPOINTS = 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 WEBHOOKENDPOINTS.test(path)

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

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

ts 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: 98: if (!ctx.user) { 99: return ctx.throw(401, "No user info found")

The bypassed controller writes attacker-derived schema data to the webhook and automation trigger outputs:

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

ts 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 64: if (webhook.action.type === WebhookActionType.AUTOMATION) { 65: let automation = await db.get<Automation>(webhook.action.target) 66: const autoOutputs = automation.definition.trigger.schema.outputs 67: let properties = webhook.bodySchema?.properties 68: // reset webhook outputs 69: autoOutputs.properties = { 70: body: autoOutputs.properties.body, 71: } 72: for (let prop of Object.keys(properties || {})) { 73: if (properties?.[prop] == null) { 74: continue 75: } 76: const def = properties[prop] 77: if (typeof def === "boolean") { 78: continue 79: } 80: autoOutputs.properties[prop] = { 81: type: def.type as AutomationIOType, 82: description: AUTOMATIONDESCRIPTION, 83: }

The route grouping suggests builder authorization was intended, but the global webhook bypass removes it.

PoC

Non-destructive validation approach:

1. Create a webhook-backed automation as a builder. 2. Record the workspace ID and webhook ID. 3. Log out or send no auth headers. 4. Send:

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

{"unauthschemaprobe":"test"}

5. Fetch the webhook as a builder and observe that bodySchema has changed. 6. 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.

— GitHub