Port 135 EPMAP
Port 135 is the IANA-assigned epmap port for DCE endpoint resolution (TCP / UDP).
What is port 135 used for?
Port 135 is assigned to epmap and uses TCP / UDP. The IANA registry describes the service as “DCE endpoint resolution”. It sits in the well-known range, which operating systems reserve for core network services, so software expects it at this number by default.
Ports are the transport-layer address a service listens on. A client that wants to reach epmap connects to port 135. A TCP connection is refused when nothing is listening, while a UDP request simply goes unanswered. That is why a port conflict appears whenever two processes try to bind the same number.
Use the commands below to confirm whether port 135 is actually in use before you change firewall rules. Blocking the port stops new inbound traffic at the firewall, but it does not stop a local process from listening, and it does not remove the service from the machine.
Source: IANA Service Name and Transport Protocol Port Number Registry. Registered assignee: [Joe_Pato].
Check and block port 135
Copy-ready commands for the protocols assigned to this port. Run the check first, then block only what should not be reachable.
Check on Linux
sudo ss -tlpn 'sport = :135'
sudo ss -ulpn 'sport = :135'Check on Windows
Get-NetTCPConnection -LocalPort 135 -State Listen -ErrorAction SilentlyContinue
Get-NetUDPEndpoint -LocalPort 135 -ErrorAction SilentlyContinueBlock with UFW
sudo ufw deny 135/tcp
sudo ufw deny 135/udpBlock with iptables
sudo iptables -A INPUT -p tcp --dport 135 -j DROP
sudo iptables -A INPUT -p udp --dport 135 -j DROPThese commands are examples for a typical host. Check the listener before you change firewall rules, and persist iptables rules with iptables-save or netfilter-persistent. On Windows, use Windows Defender Firewall or New-NetFirewallRule for persistent blocks. The iptables rules here cover IPv4; mirror them with ip6tables if IPv6 is enabled.
Is port 135 safe to expose?
Microsoft RPC endpoint mapper is a common lateral-movement target on Windows networks. Never expose it to the public internet. Treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
Where port 135 is usually used
Most traffic on port 135 falls into these scenarios. The demo below is a safe way to confirm the listener before you change anything.
- Core infrastructure that clients expect to find at its default number.
- Firewall reviews that baseline which classic services are reachable.
- Troubleshooting connectivity when an application assumes the standard port.
Probe the port
Confirm something is listening before you debug the client. Replace 127.0.0.1 with the host you are testing.
nc -vz 127.0.0.1 135Common problems with port 135
Connection refused or timed out
Refused usually means the host is reachable but nothing is listening on port 135. A timeout more often means a firewall drop, a wrong host or a service bound to a different interface.
Port already in use
Find the process holding the port with sudo ss -tlpn 'sport = :135' or sudo lsof -i :135. Stop that process or configure it to bind another port; killing it without identifying it can take down a production service.
Firewall rule did not survive a reboot
UFW and Windows Firewall keep rules across restarts. Raw iptables rules do not: save them with iptables-save or the netfilter-persistent package, and re-apply after upgrades that reset the ruleset.
The port is blocked but still reachable
A firewall rule filters inbound traffic; it does not close the listener. Confirm with the check command above and bind the service to 127.0.0.1 when only local clients need it.
Port 135 at a glance
| Port number | 135 |
|---|---|
| Service name | epmap |
| Transport protocol | TCP / UDP |
| Category | Core network services |
| Range | Well-known port (0–1023) |
| Risk level | High |
| Registered assignee | [Joe_Pato] |
| Registry description | DCE endpoint resolution |
| Source | IANA Service Name and Transport Protocol Port Number Registry |
Frequently asked questions
What is port 135 used for?
Port 135 (EPMAP) uses TCP / UDP. DCE endpoint resolution.
How do I check if port 135 is open?
On Linux run `sudo ss -tlpn 'sport = :135'` and `sudo ss -ulpn 'sport = :135'`. On Windows run `Get-NetTCPConnection -LocalPort 135 -State Listen -ErrorAction SilentlyContinue` and `Get-NetUDPEndpoint -LocalPort 135 -ErrorAction SilentlyContinue` in PowerShell. If the port is open, the output shows a process listening on port 135; empty output usually means nothing is bound to it.
How do I block port 135?
With UFW run `sudo ufw deny 135/tcp` and `sudo ufw deny 135/udp`. With iptables run `sudo iptables -A INPUT -p tcp --dport 135 -j DROP` and `sudo iptables -A INPUT -p udp --dport 135 -j DROP`. Persist the iptables rules with your distribution's netfilter-persistent or iptables-save tooling so they survive a reboot.
Is port 135 safe to expose?
Microsoft RPC endpoint mapper is a common lateral-movement target on Windows networks. Never expose it to the public internet. Nevertheless, treat this port as sensitive. Restrict it to trusted networks or a VPN, require authentication and logging, and never expose it directly to the public internet without a hardened gateway in front.
Related ports
Primary data: IANA Service Name and Transport Protocol Port Number Registry.
Last reviewed 2026-10-30 · Methodology · About · Privacy