Widespread impact: authentication bypass enables data writes to any bucket with a valid key; affects all MinIO deployments.
CVE-2026-40344
MinIO auth bypass allows writes to any bucket with a valid key, no signature.
Is CVE-2026-40344 being exploited?
Not confirmed. CVE-2026-40344 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.42% probability of exploitation in the next 30 days.
How severe is CVE-2026-40344?
CVE-2026-40344 is rated High with a CVSS score of 8.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-40344?
Yes. A fix has been recorded for CVE-2026-40344. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-40344 affect?
CVE-2026-40344 affects MinIO server (open-source). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-40344?
Upgrade to RELEASE.2026-04-11T03-20-12Z or later; or block unsigned-trailer requests; restrict WRITE.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attacker with a valid access key can write arbitrary objects to any bucket, bypassing cryptographic signature checks.
Patch when possible