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// Web

Port 8991: webmail HTTPS service

Port 8991 is assigned by IANA to https-wmap (webmail HTTPS service).

8991

How https-wmap works

Web
browser:8991https-wmap browser:8991https-wmap

A browser sends an HTTP request to port 8991 and the https-wmap server sends the page back.

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
Web
01 Security

Is port 8991 dangerous?

We have no specific security note for port 8991. Its risk depends on the program actually listening on it. General advice for web services:

  • Serve it over HTTPS only and check the HTTP security headers.
  • Keep admin consoles and development servers off the Internet.
  • Patch the application server and remove default credentials and sample apps.
02 Registry

IANA registry entries for port 8991

ServicePortTransportDescriptionReferenceUpdated
https-wmap 8991 TCP, UDP webmail HTTPS service - 2007-12-03

// source: IANA service name and port number registry

03 Check it

Which program uses port 8991, and is it reachable?

Linux

sudo ss -ltnup 'sport = :8991'      # process listening on 8991
sudo lsof -nP -i :8991

macOS

sudo lsof -nP -i :8991

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 8991 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 8991
netstat -ano | findstr :8991

From another machine

nmap -p 8991 -sV <host>
sudo nmap -sU -p 8991 <host>
nc -zv <host> 8991

Block it in the firewall

sudo ufw deny 8991/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 8991" -Direction Inbound -LocalPort 8991 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 8991 used for?

Port 8991 is assigned by IANA to https-wmap (webmail HTTPS service).

Is port 8991 TCP or UDP?

Port 8991 is registered for TCP and UDP.

Is it safe to open port 8991?

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. Serve it over HTTPS only and check the HTTP security headers.

How do I check if port 8991 is open?

On Linux run "ss -ltnup 'sport = :8991'", on macOS "lsof -nP -i :8991", and on Windows "netstat -ano | findstr :8991" to see the local process. From another machine, "nmap -p 8991 <host>" shows whether it is reachable.

05 Related
:443 HTTPS tcp · udp · sctp · low risk :80 HTTP tcp · udp · sctp · moderate risk :8080 HTTP alternate tcp · udp · high risk :8443 HTTPS alternate tcp · udp · moderate risk :3000 Dev servers / Grafana tcp · udp · moderate risk :5000 Flask / Docker registry / UPnP tcp · udp · moderate risk :8000 HTTP alternate (dev) tcp · udp · moderate risk :8888 Jupyter / HTTP alternate tcp · udp · high risk

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