8.8

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-41145

CVE-2026-41145: MinIO has an Unauthenticated Object Write via Query-String Credential Signature Bypass in Unsigned-Trailer Uploads

Impact

What kind of vulnerability is it? Who is impacted?

An authentication bypass vulnerability in MinIO's STREAMING-UNSIGNED-PAYLOAD-TRAILER code path 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.

PutObjectHandler and PutObjectPartHandler call newUnsignedV4ChunkedReader with a signature verification gate based solely on the presence of the Authorization header:

newUnsignedV4ChunkedReader(r, true, r.Header.Get(xhttp.Authorization) != "")

Meanwhile, isPutActionAllowed extracts credentials from either the Authorization header or the X-Amz-Credential query parameter, and trusts whichever it finds. An attacker omits the Authorization header and supplies credentials exclusively via the query string. The signature gate evaluates to false, doesSignatureMatch is never called, and the request proceeds with the permissions of the impersonated access key.

This affects PutObjectHandler (standard and tables/warehouse bucket paths) and PutObjectPartHandler (multipart uploads).

Affected components: cmd/object-handlers.go (PutObjectHandler), cmd/object-multipart-handlers.go (PutObjectPartHandler).

Affected Versions

All MinIO releases through the final release of the minio/minio open-source project.

The vulnerability was introduced in commit ("Signed trailers for signature v4", ), which added support. The first affected release is .

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CVE-2026-41145

CVE-2026-41145:

8.8

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
github.com/minio/minio	go	>= 0.0.0-20230506025312-76913a9fd5c6, <= 0.0.0-20260212201848-7aac2a2c5b7c

Technical Details

Vulnerability Intelligence
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Root Cause Analysis

The vulnerability is an authentication bypass in MinIO's handling of STREAMING-UNSIGNED-PAYLOAD-TRAILER requests. The core issue is that the signature verification process can be skipped if an attacker omits the Authorization header and provides credentials via query string parameters. The functions PutObjectHandler and PutObjectPartHandler are the entry points for the vulnerable operations (object creation and multipart uploads). They both call newUnsignedV4ChunkedReader, which contains the flawed logic for signature verification. The vulnerability was introduced when support for authTypeStreamingUnsignedTrailer was added. An attacker can exploit this to write arbitrary objects to any bucket if they know a valid access key, even without the corresponding secret key. The provided patch evidence from commit 76913a9fd clearly shows the introduction of this flawed logic.

Vulnerable functions

objectAPIHandlers.PutObjectHandler

cmd/object-handlers.go

This function handles `PutObject` requests. It is vulnerable because it calls `newUnsignedV4ChunkedReader` without enforcing signature verification when the `Authorization` header is omitted, allowing an attacker to upload objects without proper authentication.

objectAPIHandlers.PutObjectPartHandler

cmd/object-multipart-handlers.go

This function handles `PutObjectPart` requests for multipart uploads. It is vulnerable for the same reason as `PutObjectHandler`, as it uses `newUnsignedV4ChunkedReader` in a way that allows signature verification to be bypassed.

newUnsignedV4ChunkedReader

cmd/streaming-v4-unsigned.go

This function is called by both `PutObjectHandler` and `PutObjectPartHandler`. It is the core of the vulnerability, as it contains the logic that conditionally skips signature verification, enabling the authentication bypass.

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WAF Protection Rules

WAF Rule

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Reasoning

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8.8

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CVE-2026-41145: MinIO has an Unauthenticated Object Write via Query-String Credential Signature Bypass in Unsigned-Trailer Uploads

Impact

Affected Versions

CVE-2026-41145:

8.8

-

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Technical Details

Technical Details

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Vulnerable functions

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Reasoning

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Root Cause Analysis

Vulnerable functions

Technical Details

8.8

8.8

CVE-2026-41145: MinIO has an Unauthenticated Object Write via Query-String Credential Signature Bypass in Unsigned-Trailer Uploads

Impact

Affected Versions

Basic Information

Basic Information

Patches

Binary Downloads

FIPS Binaries

Package Downloads

Container Images

Homebrew (macOS)

Workarounds

Credits

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