Privilege Escalation on Linux/MacOS

Impact

An attacker can use crafted requests to bypass metadata bucket name checking and put an object into any bucket while processing PostPolicyBucket. To carry out this attack, the attacker requires credentials with arn:aws:s3:::* permission, as well as enabled Console API access.

Patches

commit 67f4ba154a27a1b06e48bfabda38355a010dfca5
Author: Aditya Manthramurthy <donatello@users.noreply.github.com>
Date:   Sun Mar 19 21:15:20 2023 -0700

    fix: post policy request security bypass (#16849)

Workarounds

Browser API access must be enabled turning off MINIO_BROWSER=off allows for this workaround.

References

The vulnerable code:

// minio/cmd/generic-handlers.go
func setRequestValidityHandler(h http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    // ...
    // For all other requests reject access to reserved buckets
    bucketName, _ := request2BucketObjectName(r)
    if isMinioReservedBucket(bucketName) || isMinioMetaBucket(bucketName) {
      if !guessIsRPCReq(r) && !guessIsBrowserReq(r) && !guessIsHealthCheckReq(r) && !guessIsMetricsReq(r) && !isAdminReq(r) && !isKMSReq(r) {
        if ok {
          tc.FuncName = "handler.ValidRequest"
          tc.ResponseRecorder.LogErrBody = true
        }
        writeErrorResponse(r.Context(), w, errorCodes.ToAPIErr(ErrAllAccessDisabled), r.URL)
        return
      }
    }
    // ...