CVE-2026-33419: MinIO LDAP login brute-force via user enumeration and missing rate limit

What kind of vulnerability is it? Who is impacted?

MinIO AIStor’s STS (Security Token Service) AssumeRoleWithLDAPIdentity endpoint is vulnerable to LDAP credential brute-forcing due to two combined weaknesses: (1) distinguishable error responses that enable username enumeration, and (2) absence of rate limiting on authentication attempts. An unauthenticated network attacker can enumerate valid LDAP usernames and then perform unlimited password guessing to obtain temporary AWS-style STS credentials, gaining access to the victim’s S3 buckets and objects.

All deployments with LDAP configured running an affected version are impacted.

There are two vulnerabilities:

1. User Enumeration via Distinguishable Error Messages (CWE-204)
2. Missing Rate Limiting on STS Authentication Endpoints (CWE-307)

When exploited together, an attacker can:

1. Enumerate valid LDAP usernames by observing error message differences.
2. Perform high-speed password brute-force attacks against confirmed valid users.
3. Upon finding valid credentials, obtain temporary AWS-style STS credentials (AccessKeyId, SecretAccessKey, SessionToken) with full access to the victim user’s S3 resources.