# CVE-2026-40344: MinIO has an Unauthenticated Object Write via Missing Signature Verification in Unsigned-Trailer Uploads > Attackers with a valid access key can write arbitrary objects to any bucket without signature verification due to missing checks in the Snowball auto-extract handler. - **Severity:** High 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`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 22 Apr 2026 - **Updated:** 22 Apr 2026 - **Also known as:** GHSA-9c4q-hq6p-c237, GO-2026-5284, ROOT-APP-GOBINARY-CVE-2026-40344 ## What is CVE-2026-40344? CVE-2026-40344 is a high-severity authentication bypass vulnerability in minio, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official 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. Weakness: CWE-306 (Missing Authentication for Critical Functionality), CWE-287 (Improper Authentication) ## Which versions are affected by CVE-2026-40344? 3 open source packages ship an affected version, including github.com/minio/minio. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `github.com/minio/minio` | Go | From 0.0.0-20230506025312-76913a9fd5c6 | None | | `github.com/minio/minio` | Go | From 0.0.0-20230506025312-76913a9fd5c6 to 0.0.0-20260212201848-7aac2a2c5b7c | None | | `github.com/minio/minio` | Go | From 0.0.0-20230506025312-76913a9fd5c6 to 0.0.0-20260212201848-7aac2a2c5b7c | None | Products: Minio Minio. ## How do I fix CVE-2026-40344? Upgrade to a fixed version. ## Is CVE-2026-40344 being exploited? There is no known exploitation of CVE-2026-40344 in the wild and no public exploit code. ## Other vulnerabilities in minio - [CVE-2023-28434](https://insights.sbomify.com/CVE-2023-28434/): MinIO Security Feature Bypass (high 8.8, exploited in the wild) - [CVE-2023-28432](https://insights.sbomify.com/CVE-2023-28432/): MinIO Information Disclosure (high 7.5, exploited in the wild) - [CVE-2020-11012](https://insights.sbomify.com/CVE-2020-11012/): Authentication bypass MinIO Admin API (critical 9.3) - [CVE-2026-33322](https://insights.sbomify.com/CVE-2026-33322/): MinIO: JWT Algorithm Confusion in OIDC Authentication (critical 9.2) - [CVE-2026-33419](https://insights.sbomify.com/CVE-2026-33419/): MinIO: LDAP login brute-force via user enumeration and missing rate limit (critical 9.1) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-40344 and fix it if it is affected. What it is: CVE-2026-40344 is a high-severity authentication bypass vulnerability in minio, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-40344 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/minio/minio (Go): affected from 0.0.0-20230506025312-76913a9fd5c6; no fix listed - github.com/minio/minio (Go): affected from 0.0.0-20230506025312-76913a9fd5c6 up to 0.0.0-20260212201848-7aac2a2c5b7c; no fix listed - github.com/minio/minio (Go): affected from 0.0.0-20230506025312-76913a9fd5c6 up to 0.0.0-20260212201848-7aac2a2c5b7c; no fix listed Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-40344/ (Markdown: https://insights.sbomify.com/CVE-2026-40344/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40344 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40344 - OSV: https://osv.dev/vulnerability/CVE-2026-40344 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-40344/ Summaries are generated and may contain mistakes; the official description above is the record.