CVE-2025-31489: 
MinIO vulnerability analysis and mitigation

MinIO, a High Performance Object Storage server compatible with Amazon S3, disclosed a critical security vulnerability tracked as CVE-2025-31489. The vulnerability was discovered in April 2025 and affects version RELEASE.2023-05-18T00-05-36Z. The issue involves incomplete signature validation for unsigned-trailer uploads, where the signature component of the authorization may be invalid (GitHub Advisory, Security Online).

The vulnerability stems from a flaw in how MinIO handles authorization during unsigned payload trailer uploads. The core issue lies in the signature validation process where the signature component of the authorization header can be invalid and is completely ignored by the system. The vulnerability has been assigned a CVSS 4.0 Base Score of 8.7 (HIGH) with the vector string CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N. The issue is classified under CWE-347 (Improper Verification of Cryptographic Signature) (NVD).

The vulnerability allows attackers with prior knowledge of an access key and bucket name to upload arbitrary objects to buckets where they have WRITE permissions. While the attack requires specific preconditions, including knowledge of the access key and existing write permissions, the exploitation is described as trivial and can be easily accomplished using curl commands (GitHub Advisory, Security Online).

MinIO has released a patch in version RELEASE.2025-04-03T14-56-28Z to address this vulnerability. As a temporary workaround, administrators can reject requests with x-amz-content-sha256: STREAMING-UNSIGNED-PAYLOAD-TRAILER at the load balancer layer and instruct application users to use STREAMING-AWS4-HMAC-SHA256-PAYLOAD-TRAILER instead. Given the high severity of this vulnerability, users are strongly advised to upgrade to the patched version immediately (GitHub Advisory).