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// Directory & authentication

Port 5757: OpenMail X.500 Directory Server

Port 5757 is assigned by IANA to x500ms (OpenMail X.500 Directory Server).

5757

How x500ms works

Directory & authentication
userdirectoryx500msresponse userdirectoryx500msresponse

The client proves who it is on port 5757 and gets an answer (or a ticket) it can use with other services.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Directory & authentication
01 Security

Is port 5757 dangerous?

We have no specific security note for port 5757. Its risk depends on the program actually listening on it. General advice for directory & authentication services:

  • Keep directory and authentication services on internal networks.
  • Require signing or TLS and disable anonymous queries.
  • Monitor authentication failures for spraying and brute force.
02 Registry

IANA registry entries for port 5757

ServicePortTransportDescriptionReferenceUpdated
x500ms 5757 TCP, UDP OpenMail X.500 Directory Server - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 5757, and is it reachable?

Linux

sudo ss -ltnup 'sport = :5757'      # process listening on 5757
sudo lsof -nP -i :5757

macOS

sudo lsof -nP -i :5757

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 5757 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 5757
netstat -ano | findstr :5757

From another machine

nmap -p 5757 -sV <host>
sudo nmap -sU -p 5757 <host>
nc -zv <host> 5757

Block it in the firewall

sudo ufw deny 5757/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 5757" -Direction Inbound -LocalPort 5757 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 5757 used for?

Port 5757 is assigned by IANA to x500ms (OpenMail X.500 Directory Server).

Is port 5757 TCP or UDP?

Port 5757 is registered for TCP and UDP.

Is it safe to open port 5757?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Keep directory and authentication services on internal networks.

How do I check if port 5757 is open?

On Linux run "ss -ltnup 'sport = :5757'", on macOS "lsof -nP -i :5757", and on Windows "netstat -ano | findstr :5757" to see the local process. From another machine, "nmap -p 5757 <host>" shows whether it is reachable.

05 Related
:389 LDAP tcp · udp · high risk :636 LDAPS tcp · udp · moderate risk :88 Kerberos tcp · udp · high risk :3268 Global Catalog (LDAP) tcp · udp · high risk :1812 RADIUS udp · tcp · moderate risk :31 MSG Authentication tcp · udp :49 Login Host Protocol (TACACS) tcp · udp :56 XNS Authentication tcp · udp

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