Summary
The file upload endpoint POST /api/attachments/process does not enforce active-content restrictions for authenticated users. The checks for dangerous file extensions (html, svg, js, php, etc.) are conditionally wrapped inside if (isPublicUser) or if (isPublicUser || !env.SELF_HOSTED), meaning any authenticated builder can upload executable web content — SVG files with inline <script> tags, HTML pages with JavaScript, .js modules — which are then stored in the object store (MinIO/S3) with their correct MIME types (image/svg+xml, text/html, application/javascript). When the resulting signed URL is opened by any app user, the browser executes the payload.
Impact is persistent stored XSS over all application end users.
Details
The vulnerability exists in a single handler function uploadFile shared by two routes, located in packages/server/src/api/controllers/static/index.ts (lines 93–179).
Route definitions (packages/server/src/api/routes/static.ts):
POST /api/attachments/process → authorized(BUILDER)
POST /api/attachments/:tableId/upload → authorized(PermissionType.TABLE, PermissionLevel.WRITE)
Both routes invoke the same uploadFile function. The second endpoint is accessible to any authenticated app user (BASIC or POWER role) who has been granted WRITE on any table — not just builders.
PoC
Prerequisites
- Budibase self-hosted Docker deployment, any version ≤ 3.30.6
- An account with Builder role (does not require admin)
- Target app published and accessible to end users
Step 1 — Authenticate as builder
POST /api/global/auth/default/login HTTP/1.1
Host: target:10000
Content-Type: application/json
{"username":"builder@company.com","password":"BuilderPass1!"}HTTP/1.1 200 OK
Set-Cookie: budibase:auth=<jwt>; path=/; expires=Tue, 19 Jan 2038 03:14:07 GMT
Set-Cookie: budibase:auth.sig=<sig>; path=/; expires=Tue, 19 Jan 2038 03:14:07 GMT
{"message":"Login successful"}
The CSRF token is bound to the session. Browsers send it automatically via the Budibase
frontend JS. For scripted requests, decode the JWT payload (base64url second segment) to
extract sessionId, then read the Redis key session-<userId>/<sessionId> → csrfToken.
Step 2 — Upload SVG with XSS payload
POST /api/attachments/process HTTP/1.1
Host: target:10000
Cookie: budibase:auth=<jwt>; budibase:auth.sig=<sig>
x-budibase-app-id: <dev_app_id>
x-csrf-token: <csrf_token>
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryXXXXXXXXXXXXXXXX
Content-Length: 391
------WebKitFormBoundaryXXXXXXXXXXXXXXXX
Content-Disposition: form-data; name="file"; filename="xss.svg"
Content-Type: image/svg+xml
<svg xmlns="http://www.w3.org/2000/svg"><script>alert(document.domain)</script></svg>
------WebKitFormBoundaryXXXXXXXXXXXXXXXX--
HTTP/1.1 200 OK
[{"size":207,"name":"xss.svg","url":"http://target:10000/files/signed/.../<uuid>.svg?X-Amz-...","extension":"svg","key":"workspace_id/attachments/<uuid>.svg"}]Impact
- App end users - Stored XSS on any screen containing the attachment URL. Session cookie theft → full account takeover. |
- Builder accounts - If malicious URL is shared within the workspace (table attachment, embedded image), XSS fires in builder's session → workspace takeover.
Discovered By:
Abdulrahman Albatel
Abdullah Alrasheed
References
da7om85 Reporter
Summary
The file upload endpoint
POST /api/attachments/processdoes not enforce active-content restrictions for authenticated users. The checks for dangerous file extensions (html,svg,js,php, etc.) are conditionally wrapped insideif (isPublicUser)orif (isPublicUser || !env.SELF_HOSTED), meaning any authenticated builder can upload executable web content — SVG files with inline<script>tags, HTML pages with JavaScript,.jsmodules — which are then stored in the object store (MinIO/S3) with their correct MIME types (image/svg+xml,text/html,application/javascript). When the resulting signed URL is opened by any app user, the browser executes the payload.Impact is persistent stored XSS over all application end users.
Details
The vulnerability exists in a single handler function uploadFile shared by two routes, located in packages/server/src/api/controllers/static/index.ts (lines 93–179).
Route definitions (packages/server/src/api/routes/static.ts):
POST /api/attachments/process → authorized(BUILDER)
POST /api/attachments/:tableId/upload → authorized(PermissionType.TABLE, PermissionLevel.WRITE)
Both routes invoke the same uploadFile function. The second endpoint is accessible to any authenticated app user (BASIC or POWER role) who has been granted WRITE on any table — not just builders.
PoC
Prerequisites
Step 1 — Authenticate as builder
The CSRF token is bound to the session. Browsers send it automatically via the Budibase
frontend JS. For scripted requests, decode the JWT payload (base64url second segment) to
extract
sessionId, then read the Redis keysession-<userId>/<sessionId>→csrfToken.Step 2 — Upload SVG with XSS payload
Impact
Discovered By:
Abdulrahman Albatel
Abdullah Alrasheed
References