macOS Network Services & Protocols
Last updated
Last updated
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These are the common macOS services to access them remotely.
You can enable/disable these services in System Settings --> Sharing
VNC, known as “Screen Sharing” (tcp:5900)
SSH, called “Remote Login” (tcp:22)
Apple Remote Desktop (ARD), or “Remote Management” (tcp:3283, tcp:5900)
AppleEvent, known as “Remote Apple Event” (tcp:3031)
Check if any is enabled running:
Apple Remote Desktop (ARD) is an enhanced version of Virtual Network Computing (VNC) tailored for macOS, offering additional features. A notable vulnerability in ARD is its authentication method for the control screen password, which only uses the first 8 characters of the password, making it prone to brute force attacks with tools like Hydra or GoRedShell, as there are no default rate limits.
Vulnerable instances can be identified using nmap's vnc-info script. Services supporting VNC Authentication (2) are especially susceptible to brute force attacks due to the 8-character password truncation.
To enable ARD for various administrative tasks like privilege escalation, GUI access, or user monitoring, use the following command:
ARD provides versatile control levels, including observation, shared control, and full control, with sessions persisting even after user password changes. It allows sending Unix commands directly, executing them as root for administrative users. Task scheduling and Remote Spotlight search are notable features, facilitating remote, low-impact searches for sensitive files across multiple machines.
Bonjour, an Apple-designed technology, allows devices on the same network to detect each other's offered services. Known also as Rendezvous, Zero Configuration, or Zeroconf, it enables a device to join a TCP/IP network, automatically choose an IP address, and broadcast its services to other network devices.
Zero Configuration Networking, provided by Bonjour, ensures that devices can:
Automatically obtain an IP Address even in the absence of a DHCP server.
Perform name-to-address translation without requiring a DNS server.
Discover services available on the network.
Devices using Bonjour will assign themselves an IP address from the 169.254/16 range and verify its uniqueness on the network. Macs maintain a routing table entry for this subnet, verifiable via netstat -rn | grep 169.
For DNS, Bonjour utilizes the Multicast DNS (mDNS) protocol. mDNS operates over port 5353/UDP, employing standard DNS queries but targeting the multicast address 224.0.0.251. This approach ensures that all listening devices on the network can receive and respond to the queries, facilitating the update of their records.
Upon joining the network, each device self-selects a name, typically ending in .local, which may be derived from the hostname or randomly generated.
Service discovery within the network is facilitated by DNS Service Discovery (DNS-SD). Leveraging the format of DNS SRV records, DNS-SD uses DNS PTR records to enable the listing of multiple services. A client seeking a specific service will request a PTR record for <Service>.<Domain>, receiving in return a list of PTR records formatted as <Instance>.<Service>.<Domain> if the service is available from multiple hosts.
The dns-sd utility can be employed for discovering and advertising network services. Here are some examples of its usage:
To search for SSH services on the network, the following command is used:
This command initiates browsing for _ssh._tcp services and outputs details such as timestamp, flags, interface, domain, service type, and instance name.
To advertise an HTTP service, you can use:
This command registers an HTTP service named "Index" on port 80 with a path of /index.html.
To then search for HTTP services on the network:
When a service starts, it announces its availability to all devices on the subnet by multicasting its presence. Devices interested in these services don't need to send requests but simply listen for these announcements.
For a more user-friendly interface, the Discovery - DNS-SD Browser app available on the Apple App Store can visualize the services offered on your local network.
Alternatively, custom scripts can be written to browse and discover services using the python-zeroconf library. The python-zeroconf script demonstrates creating a service browser for _http._tcp.local. services, printing added or removed services:
If there are concerns about security or other reasons to disable Bonjour, it can be turned off using the following command:
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