MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

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

EPSS

• CVE-2026-40344: 0.42% estimated exploitation activity in the next 30 days; percentile 36.21 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Two authentication bypass vulnerabilities in MinIO's STREAMING-UNSIGNED-PAYLOAD-TRAILER code path allow any user who knows a valid access key to write arbitrary objects to any bucket without knowing the secret key or providing a valid cryptographic signature. Any MinIO deployment is impacted. The attack requires only a valid access key (the well-known default minioadmin, or any key with WRITE permission on a bucket) and a target bucket name. There are two vulnerabilities: 1. Missing Signature Verification in PutObjectExtractHandler / Snowball (CWE-306) 2. Signature Verification Bypass via Query-String Credentials (CWE-287) Vulnerability 1 — Missing signature verification in PutObjectExtractHandler (Snowball) When authTypeStreamingUnsignedTrailer support was added (commit 76913a9fd, PR #16484), the new auth type was handled in PutObjectHandler and PutObjectPartHandler but was never added to PutObjectExtractHandler. The snowball auto-extract handler's switch rAuthType block has…

Published by the source

14 Apr 2026, 00:04 UTC

Last modified by the source

5 May 2026, 15:43 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9c4q-hq6p-c237

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# Patch Next advisory brief: CVE-2026-40344

Advisory: MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads
IDs: CVE-2026-40344, GHSA-9c4q-hq6p-c237
Record: https://patchnext.com/advisories/cve-2026-40344 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/minio/minio: affected >= 0.0.0-20230506025312-76913a9fd5c6, <= 0.0.0-20260212201848-7aac2a2c5b7c

## Suggested inspection (read-only)
- Go github.com/minio/minio: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/minio/minio.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9c4q-hq6p-c237 (GitHub-reviewed advisory GHSA-9c4q-hq6p-c237 lists affected ranges: Go github.com/minio/minio >=0.0.0-20230506025312-76913a9fd5c6 <=0.0.0-20260212201848-7aac2a2c5b7c)

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