Budibase 3.39.4 before 3.40.0 Authorization Regression via S3 Presigned URL

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Budibase versions 3.39.4 before 3.40.0 contain an authorization regression in the S3 attachment upload endpoint that allows BASIC users to obtain S3 PutObject presigned URLs by sending POST requests to the attachments endpoint. The route was changed from a BUILDER permission check to a TABLE/WRITE check, which BASIC users hold by default. Attackers can specify arbitrary S3 buckets in the request body to generate presigned URLs for writing to any bucket accessible by the stored IAM credentials, enabling unauthorized file uploads.

Source published

14 Aug 2026 11:35:43 UTC

Source modified

8 Oct 2026 15:24:37 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N

CVSS 3.1 · 7.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

Budibase versions 3.39.4 before 3.40.0 contain an authorization regression in the S3 attachment upload endpoint that allows BASIC users to obtain S3 PutObject presigned URLs by sending POST requests to the attachments endpoint. The route was changed from a BUILDER permission check to a TABLE/WRITE check, which BASIC users hold by default. Attackers can specify arbitrary S3 buckets in the request body to generate presigned URLs for writing to any bucket accessible by the stored IAM credentials, enabling unauthorized file uploads.

Source published

Aug 14, 2026, 11:35:43 AM (timezone not stated)

Source modified

Oct 8, 2026, 3:24:37 PM (timezone not stated)

Observed here

9 Nov 2026 15:08:48 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N

Budibase versions 3.39.4 before 3.40.0 contain an authorization regression in the S3 attachment upload endpoint that allows BASIC users to obtain S3 PutObject presigned URLs by sending POST requests to the attachments endpoint. The route was changed from a BUILDER permission check to a TABLE/WRITE check, which BASIC users hold by default. Attackers can specify arbitrary S3 buckets in the request body to generate presigned URLs for writing to any bucket accessible by the stored IAM credentials, enabling unauthorized file uploads.

Source published

14 Aug 2026 12:16:47 UTC

Source modified

8 Oct 2026 16:17:37 UTC

Observed here

25 Oct 2026 15:19:03 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.3 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Secondary · 7.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

## Impact In Budibase v3.39.4, a regression in the authorization level for the S3 attachment upload endpoint allows any BASIC app user to obtain S3 PutObject presigned URLs. The endpoint uses TABLE/WRITE permission level instead of the intended BUILDER level defined in v3.39.3. Additionally, the controller does not pin the target bucket to the datasource's configured bucket, allowing writes to any S3 bucket the stored IAM credentials can access. ## Reproduction 1. As a BASIC app user, discover or obtain a valid S3 datasource ID within the app 2. Send a POST request: ``` POST /api/attachments/<datasourceId>/url Content-Type: application/json x-budibase-app-id: <appId> {"bucket": "target-bucket", "key": "malicious-file.html"} ``` 3. The response contains a valid S3 PutObject presigned URL 4. Use the presigned URL to upload arbitrary content to any writable S3 bucket in the IAM credential scope ## Root Cause The `/api/attachments/:datasourceId/url` route was changed from `authorized(BUILDER)` in v3.39.3 to `authorized(PermissionType.TABLE, PermissionLevel.WRITE)` in v3.39.4. BASIC users have TABLE/WRITE permissions by default, so they can call this endpoint. The controller at `packages/server/src/api/controllers/static/index.ts:614-632` accepts the `bucket` parameter directly from the request body and passes it to `getSignedUrl` without validating against the datasource's configured bucket. ## Evidence The test suite at `packages/server/src/api/routes/tests/static.spec.ts:218-235` confirms this behavior. The test authenticates as a BASIC role user and successfully generates a signed upload URL, verifying HTTP 200 and a defined `res.body.signedUrl`. ## Remediation 1. Restore the `authorized(BUILDER)` middleware on the route 2. Add `paramResource("datasourceId")` to ensure the datasource belongs to the caller's app 3. Pin the S3 bucket to `datasource.config.bucket` in the controller, ignoring the caller-supplied bucket value

Source published

24 Jul 2026 21:17:03 UTC

Source modified

15 Aug 2026 05:19:24 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

Publisher rating · HIGH