CVE-2026-40344
MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads
Description
MinIO is a high-performance object storage system. Starting in RELEASE.2023-05-18T00-05-36Z and prior to RELEASE.2026-04-11T03-20-12Z, an authentication bypass vulnerability in MinIO's Snowball auto-extract handler (`PutObjectExtractHandler`) allows 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. When `authTypeStreamingUnsignedTrailer` support was added, 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 no case for `authTypeStreamingUnsignedTrailer`, so execution falls through with zero signature verification. The `isPutActionAllowed` call before the switch extracts the access key and checks IAM permissions, but does not verify the cryptographic signature. An attacker sends a PUT request with `X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER`, `X-Amz-Meta-Snowball-Auto-Extract: true`, and an `Authorization` header containing a valid access key with a completely fabricated signature. The request is accepted and the tar payload is extracted into the bucket. Users of the open-source minio/minio project should upgrade to MinIO AIStor RELEASE.2026-04-11T03-20-12Z or later. If upgrading is not immediately possible, block unsigned-trailer requests at the load balancer. Reject any request containing X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER at the reverse proxy or WAF layer. Clients can use STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER (the signed variant) instead. Alternatively, restrict WRITE permissions. Limit s3:PutObject grants to trusted principals. While this reduces the attack surface, it does not eliminate the vulnerability since any user with WRITE permission can exploit it with only their access key.
INFO
Published Date :
April 22, 2026, 1:16 a.m.
Last Modified :
Nov. 11, 2026, 11:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Upgrade MinIO to RELEASE.2026-04-11T03:20:12Z or later.
- Block unsigned trailer requests at load balancer.
- Reject requests with STREAMING-UNSIGNED-PAYLOAD-TRAILER header.
- Restrict WRITE permissions to trusted principals.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-40344.
| URL | Resource |
|---|---|
| https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091 | Patch |
| https://github.com/minio/minio/pull/16484 | Issue Tracking |
| https://github.com/minio/minio/security/advisories/GHSA-9c4q-hq6p-c237 | Patch Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-40344 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-40344
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-40344 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-40344 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Translated by [email protected]
Nov. 11, 2026
Action Type Old Value New Value Added Translation Title: Minio, Description: MinIO es un sistema de almacenamiento de objetos de alto rendimiento. A partir de RELEASE.2023-05-18T00-05-36Z y antes de RELEASE.2026-04-11T03-20-12Z, una vulnerabilidad de omisión de autenticación en el gestor de autoextracción Snowball de MinIO (’PutObjectExtractHandler’) permite a cualquier usuario que conozca una clave de acceso válida escribir objetos arbitrarios en cualquier bucket sin conocer la clave secreta o proporcionar una firma criptográfica válida. Cualquier despliegue de MinIO está afectado. El ataque requiere solo una clave de acceso válida (el valor predeterminado conocido ’minioadmin’, o cualquier clave con permiso de ESCRITURA en un bucket) y un nombre de bucket de destino. Cuando se añadió el soporte para ’authTypeStreamingUnsignedTrailer’, el nuevo tipo de autenticación se manejó en ’PutObjectHandler’ y ’PutObjectPartHandler’ pero nunca se añadió a ’PutObjectExtractHandler’. El bloque ’switch rAuthType’ del gestor de autoextracción snowball no tiene un caso para ’authTypeStreamingUnsignedTrailer’, por lo que la ejecución continúa sin verificación de firma. La llamada ’isPutActionAllowed’ antes del switch extrae la clave de acceso y verifica los permisos de IAM, pero no verifica la firma criptográfica. Un atacante envía una solicitud PUT con ’X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER’, ’X-Amz-Meta-Snowball-Auto-Extract: true’, y un encabezado ’Authorization’ que contiene una clave de acceso válida con una firma completamente fabricada. La solicitud es aceptada y la carga útil tar se extrae en el bucket. Los usuarios del proyecto de código abierto minio/minio deberían actualizar a MinIO AIStor RELEASE.2026-04-11T03-20-12Z o posterior. Si la actualización no es posible de inmediato, bloquee las solicitudes de tráiler sin firmar en el balanceador de carga. Rechace cualquier solicitud que contenga X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER en el proxy inverso o la capa WAF. Los clientes pueden usar STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER (la variante firmada) en su lugar. Alternativamente, restrinja los permisos de ESCRITURA. Limite las concesiones s3:PutObject a principales de confianza. Si bien esto reduce la superficie de ataque, no elimina la vulnerabilidad ya que cualquier usuario con permiso de ESCRITURA puede explotarla con solo su clave de acceso. -
CVE Modified by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'minio', 'product': 'minio', 'versions': [{'status': 'affected', 'version': '>= RELEASE.2023-05-18T00-05-36Z, < RELEASE.2026-04-11T03-20-12Z'}]}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-40344', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-04-22T17:54:45.957595Z'} -
Initial Analysis by [email protected]
Apr. 27, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L Added CPE Configuration OR *cpe:2.3:a:minio:minio:*:*:*:*:*:*:*:* versions from (including) 2023-05-18t00-05-36z up to (excluding) 2026-04-11T03-20-12Z Added Reference Type GitHub, Inc.: https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/minio/minio/pull/16484 Types: Issue Tracking Added Reference Type GitHub, Inc.: https://github.com/minio/minio/security/advisories/GHSA-9c4q-hq6p-c237 Types: Patch, Vendor Advisory -
New CVE Received by [email protected]
Apr. 22, 2026
Action Type Old Value New Value Added Description MinIO is a high-performance object storage system. Starting in RELEASE.2023-05-18T00-05-36Z and prior to RELEASE.2026-04-11T03-20-12Z, an authentication bypass vulnerability in MinIO's Snowball auto-extract handler (`PutObjectExtractHandler`) allows 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. When `authTypeStreamingUnsignedTrailer` support was added, 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 no case for `authTypeStreamingUnsignedTrailer`, so execution falls through with zero signature verification. The `isPutActionAllowed` call before the switch extracts the access key and checks IAM permissions, but does not verify the cryptographic signature. An attacker sends a PUT request with `X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER`, `X-Amz-Meta-Snowball-Auto-Extract: true`, and an `Authorization` header containing a valid access key with a completely fabricated signature. The request is accepted and the tar payload is extracted into the bucket. Users of the open-source minio/minio project should upgrade to MinIO AIStor RELEASE.2026-04-11T03-20-12Z or later. If upgrading is not immediately possible, block unsigned-trailer requests at the load balancer. Reject any request containing X-Amz-Content-Sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER at the reverse proxy or WAF layer. Clients can use STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER (the signed variant) instead. Alternatively, restrict WRITE permissions. Limit s3:PutObject grants to trusted principals. While this reduces the attack surface, it does not eliminate the vulnerability since any user with WRITE permission can exploit it with only their access key. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/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 Added CWE CWE-287 Added CWE CWE-306 Added Reference https://github.com/minio/minio/commit/76913a9fd5c6e5c2dbd4e8c7faf56ed9e9e24091 Added Reference https://github.com/minio/minio/pull/16484 Added Reference https://github.com/minio/minio/security/advisories/GHSA-9c4q-hq6p-c237