What causes "failed to upload Packer release zip: %s" in hashicorp/packer?

Check PACKER_LOG=1 output for the wrapped communicator error and fix the root transport issue (connection, auth, timeout).

hashicorp/packer · error

failed to upload Packer release zip: %s

Error message

failed to upload Packer release zip: %s

What it means

This error wraps a failure of comm.Upload when copying the Packer release zip from the host to C:\Windows\Temp\packer-sbom-runner.zip on the Windows guest. It is thrown at provisioner/hcp-sbom/provisioner.go:509 in uploadScanner (Windows path), called by provisionWithNativeGeneration. It indicates the communicator (typically WinRM) accepted the operation but the transfer failed, with the underlying transport error embedded.

Source

Thrown at provisioner/hcp-sbom/provisioner.go:509

	} else {
		binaryName = "packer"
		remotePath = "/tmp/packer-sbom-runner"
	}

	if isWindows {
		remoteDir := "C:\\Windows\\Temp"
		remoteZipPath := remoteDir + "\\packer-sbom-runner.zip"

		// Step 1: upload zip to remote.
		zipFile, err := os.Open(localZipPath)
		if err != nil {
			return "", fmt.Errorf("failed to open Packer release zip: %s", err)
		}
		defer func() { _ = zipFile.Close() }()

		log.Printf("[INFO] Uploading Packer release zip to %s...", remoteZipPath)
		if err := comm.Upload(remoteZipPath, zipFile, nil); err != nil {
			return "", fmt.Errorf("failed to upload Packer release zip: %s", err)
		}

		// Single PowerShell command: extract, move binary, remove zip.
		psCmd := fmt.Sprintf(
			`powershell -NoProfile -ExecutionPolicy Bypass -Command `+
				`"$ErrorActionPreference='Stop'; `+
				`Expand-Archive -Path '%s' -DestinationPath '%s' -Force; `+
				`if (!(Test-Path '%s\%s')) { throw 'packer.exe not found after extraction' }; `+
				`Move-Item -Force '%s\%s' '%s'; `+
				`Remove-Item -Force '%s'"`,
			remoteZipPath, remoteDir,
			remoteDir, binaryName,
			remoteDir, binaryName, remotePath,
			remoteZipPath,
		)
		if err := p.runRemoteCmd(ctx, comm, psCmd, "extract scanner (Windows)"); err != nil {
			return "", err
		}

View on GitHub (pinned to eb36e3c3e4)

Solutions

Check PACKER_LOG=1 output for the wrapped communicator error and fix the root transport issue (connection, auth, timeout).
Increase the communicator timeout (winrm_timeout) and retry the build — large uploads over slow networks often need more time.
Confirm the Windows guest has free disk space in C:\Windows\Temp and that no antivirus/EDR blocks Packer writing there.
Verify WinRM connectivity and credentials (winrm_username/winrm_password, port 5985/5986) before the build.
Retry the build; transient network drops during upload are a common cause and a fresh run may succeed.

Example fix

// before
source "null" "win" {
  communicator = "winrm"
  winrm_timeout = "30m" // may be too short for big zips
}
// after
source "null" "win" {
  communicator  = "winrm"
  winrm_timeout = "2h"
  winrm_use_ntlm = true
}

Defensive patterns

Strategy: retry

Validate before calling

// before build: confirm WinRM reachable
timeout := 10 * time.Second
conn, err := net.DialTimeout("tcp", fmt.Sprintf("%s:5985", guestHost), timeout)
if err != nil {
	return fmt.Errorf("WinRM not reachable on %s:5985: %w", guestHost, err)
}
conn.Close()
// confirm disk space on guest during provisioning
dfCmd := `powershell -Command "(Get-PSDrive C).Free"`

Try / catch

err := comm.Upload(remoteZipPath, zipFile, nil)
if err != nil {
	var netErr net.Error
	if errors.As(err, &netErr) && netErr.Timeout() {
		// increase winrm_timeout and retry upload
	}
	return fmt.Errorf("failed to upload Packer release zip: %w", err)
}

Prevention

Set a generous winrm_timeout sized for your zip size and network bandwidth.
Pre-check guest disk free space in C:\Windows\Temp in an early provisioner step.
Validate WinRM credentials and firewall rules (5985/5986) before long builds.
Retry transient upload failures with backoff rather than failing the whole build.
Keep release zips small or host the binary on a local mirror to reduce transfer time.

When it happens

Trigger: comm.Upload(remoteZipPath, zipFile, nil) returns an error during the Windows branch of uploadScanner — e.g. WinRM/SSH connection dropped mid-transfer, authentication failure, guest disk full in C:\Windows\Temp, or a timeout uploading a large zip.

Common situations: Unstable or slow WinRM connectivity to the Windows VM; the guest ran out of disk space in C:\Windows\Temp; wrong WinRM credentials/ports in the communicator block; security software on the guest blocking writes to Windows\Temp; transfer timeouts on large release zips over high-latency networks.

Related errors

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/72d983b1d47c8f28. Report an issue: GitHub.