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CVE-2026-40344— MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads

Quick assessment

Affected
minio minio
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

MinIO是美国MinIO公司的一款开源的对象存储服务器。该产品支持构建用于机器学习、分析和应用程序数据工作负载的基础架构。 MinIO RELEASE.2023-05-18T00-05-36Z至RELEASE.2026-04-11T03-20-12Z之前版本存在授权问题漏洞，该漏洞源于Snowball自动提取处理程序存在身份验证绕过，允许任何知道有效访问密钥的用户在不知道密钥或提供有效加密签名的情况下向任何存储桶写入任意对象。

AI Predicted 8.1 Difficulty: Trivial EPSS 0.71% · P53
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I. Basic Information for CVE-2026-40344

Vulnerability Information
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Vulnerability Title
MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
认证机制不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
MinIO 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
MinIO是美国MinIO公司的一款开源的对象存储服务器。该产品支持构建用于机器学习、分析和应用程序数据工作负载的基础架构。 MinIO RELEASE.2023-05-18T00-05-36Z至RELEASE.2026-04-11T03-20-12Z之前版本存在授权问题漏洞，该漏洞源于Snowball自动提取处理程序存在身份验证绕过，允许任何知道有效访问密钥的用户在不知道密钥或提供有效加密签名的情况下向任何存储桶写入任意对象。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
minio minio >= RELEASE.2023-05-18T00-05-36Z, < RELEASE.2026-04-11T03-20-12Z -

II. Public POCs for CVE-2026-40344

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III. Intelligence Information for CVE-2026-40344

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Patches & Fixes for CVE-2026-40344 (1)

Vendor Advisories for CVE-2026-40344 (1)

IV. Related Vulnerabilities

Same product: minio
Same vendor: minio
Same weakness: CWE-287

V. Comments for CVE-2026-40344

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