What is the C$ share?
C$ is a hidden administrative share that Windows creates automatically for the root of the C: drive. Windows makes one for every fixed drive (D$, E$ and so on) so administrators can reach a computer's files over the network without setting up a share first. The dollar sign at the end of the name hides the share from network browsing, so it doesn't appear when someone views the computer's shares in File Explorer.
Connecting to C$
Type the UNC path in File Explorer's address bar or the Run box, or map it to a drive letter:
\\PC01\C$opens the C: drive of the computer named PC01.net use Z: \\PC01\C$maps it as drive Z:.
It works only for accounts in the remote computer's local Administrators group (in a domain, Domain Admins are members by default). The remote PC must also allow File and Printer Sharing through its firewall, since the connection uses SMB on TCP port 445. On workgroup computers, where every account is local, UAC remote restrictions stop administrator accounts other than the built-in Administrator from using admin shares over the network, a common cause of "access denied".
Other administrative shares
| Share | Points to | Used for |
|---|---|---|
| C$, D$ and so on | The root of each fixed drive | Remote file access for administrators |
| ADMIN$ | The Windows folder, usually C:\Windows | Remote administration and software deployment tools |
| IPC$ | No folder: inter-process communication (named pipes) | Remote management connections between computers |
Run net share to list every share on a computer, hidden ones included, or open Computer Management and go to Shared Folders, then Shares. Any share you create can be hidden the same way, by ending its name with $.
Security considerations
Admin shares are handy for support, but an attacker who steals an administrator's password can use them to copy files and tools between machines and spread across a network. Limit who is a local administrator, give each PC a different local admin password, and block SMB from untrusted networks. Removing C$ with net share C$ /delete lasts only until the next restart; to stop Windows from recreating it, set the AutoShareWks registry value (AutoShareServer on servers) to 0 under HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters. Some management and backup tools rely on admin shares, so test before turning them off.
For the CompTIA A+ exams
Administrative shares come up with Windows networking in Core 2 (220-1202), which covers shares, mapped drives and permissions (objectives 1.7 and 2.2), and in this course's file share server lesson for Core 1 (220-1201) objective 2.3. Remember that a $ at the end of a share name hides it, that C$ and ADMIN$ need administrator rights, and that the UNC format is \\computername\sharename.