CVE-2026-34204

In MinIO up to RELEASE.2025-10-15T17-29-55Z, the globalDeploymentID/SessionTokenAuthenticate function in cmd/common-main.go of the Embedded Console component uses a hard-coded cryptographic key. The attack can be launched remotely and the exploit has been publicly disclosed.

MinIO through 7aac2a2 does not verify that every x-amz-* header present on a request also appears in the client-supplied X-Amz-SignedHeaders list. extractSignedHeaders() in cmd/signature-v4-utils.go iterates only the claimed list and never enumerates the headers that actually arrived, so an unsigned header is neither hashed into the canonical request nor rejected. Because cmd/api-router.go dispatches CopyObject on the presence of x-amz-copy-source alone, the holder of a presigned PUT URL scoped to a single object can add that header to the unmodified URL and cause a server-side copy, executed as the signer, of any object the signing key can read. A grant to write one object becomes a read of every bucket that key can reach. Amazon S3 rejects the equivalent request with HTTP 403 AccessDenied. The minio/minio GitHub repository was archived in April 2026; pgsty/silo before 1233254 is also affected.

MinIO from RELEASE.2018-08-18T03-49-57Z to before RELEASE.2025-12-20T04-58-37Z is vulnerable to memory exhaustion when processing CSV files containing lines longer than available memory. The CSV reader's nextSplit() function calls bufio.Reader.ReadBytes('\n') with no size limit, buffering the entire input in memory until a newline is found. A CSV file with no newline characters causes the entire contents to be read into a single allocation, leading to an OOM crash of the MinIO server process. This is exploitable by any authenticated user with s3:PutObject and s3:GetObject permissions. The attack is especially practical when combined with compression: a ~2 MB gzip-compressed CSV can decompress to gigabytes of data without newlines.

In MinIO all versions prior to RELEASE.2025-10-15T17-29-55Z, a privilege escalation vulnerability allows service accounts and STS accounts with restricted session policies to bypass their inline policy restrictions when performing operations on their own account, specifically when creating new service accounts for the same user. The flaw exists in the IAM policy validation logic where the code incorrectly relied on the DenyOnly argument when validating session policies for restricted accounts.