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HIGH

CVE-2026-40344

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

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…

Published Updated Sources: cvelistV5, GitHub_M

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Unreported

no source claims exploitation

EPSS

1%

chance of exploitation in 30 days

Affects

minio

minio

CVSS base

8.8

HIGH

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

None

none · proof-of-concept · active

Automatable

Yes

can an attacker script all four kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Affected scope

The catalog records vendors and products as separate lists, not pairs, so which product belongs to which vendor is not something this page can say.

Vendors (1)

minio

Products (1)

minio

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactSource
8.8CVSS 4.0HIGH——cvelistV5

Weakness & attack patterns

  • CWE-287
  • CWE-306

Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.

  • T1548Abuse Elevation Control Mechanism
  • T1040Network Sniffing
  • T1185Browser Session Hijacking

References

3 on the record

Elsewhere on this site

  • minioevery CVE for this vendor
  • CWE-287other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.