Document Correlation Attack

_posts/2026-01-22-Mitigate-Correlation.md

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+---
+layout: post
+title: "Mitigating User Tracking Caused By Correlation Attack"
+lang: "en"
+author: "rdica"
+heading: "Mitigating User Tracking Caused By Correlation Attack"
+---
+
+By default the Jamulus protocol does not map usernames to IP addresses in any publicly available data.  
+However it is possible to execute a correlation attack to achieve user<‐>IP mapping.  
+This was first reported to Jamulus developers here: [https://github.com/orgs/jamulussoftware/discussions/3545](https://github.com/orgs/jamulussoftware/discussions/3545)
+
+<!--more-->
+
+## Scope
+
+This document will attempt to summarize the problem, and provide mitigations for both users, and server admins.
+
+## The Problem - Pings and Join Events
+
+### Pings
+
+When a user attempts to connect to a server, they open the Connect dialog window. The client will **start** sending &ldquo;pings&rdquo; to every server listed in that genre to report delay latency &lpar;basically network distance&rpar; to those servers.
+
+Anyone running a server can capture those &ldquo;pings&rdquo; using tools like `tcpdump` or `tshark/wireshark` and view the IP addresses of the clients that are sending them.  
+**No username data is sent.** This is part of the Jamulus protocol, by design, to maintain a level of privacy and prevent others from finding the IP addresses of specific users.
+
+### Join Events
+
+A user will either select a server from the list, or type in a server address:port, click Connect or hit Enter, and the client will then attempt to connect to the server. At this point the client **stops** sending the &ldquo;pings&rdquo; and the client typically completes the connection to the server.
+
+Each genre has a directory server. The purpose of the directory server is to provide clients with a listing of servers registered to it, and the users connected to each server. This is public data, and viewed in the Connect dialog window, and available through a number of websites, like [explorer.jamulus.io](https://explorer.jamulus.io) or [jamulusjams.com](https://jamulusjams.com).
+
+Anyone can run an explorer instance. An explorer queries each genres directory server to get a list of servers, then queries each server directly to get a list of connected users. This is public data. **There is no IP address information on users, just the user profile data**. Again this is by design to prevent IP&lt;&dash;&gt;username mapping.  This data can also be saved for later processing.
+
+### Correlation Attack
+
+Anyone can run servers **and** explorer instances.  
+Using IPs captured by a server, one can correlate **when an IP address stops pinging** &lpar;ie; just connected to a server&rpar; and **when a new client joined a server** &lpar;username data from explorer query directly to a jamulus server&rpar; to produce an IP&lt;&dash;&gt;username mapping. The IP address can then be processed to provide geolocation data. From this one can determine the location of a specific user.
+
+## The Current Correlation Attack (as of 20260122)
+
+### Listeners
+
+There are seven servers on public Jamulus space, one in each genre. They are named ***Duet***, and have a userlimit set at two. They all share the same IP and each sit on different ports.  
+These servers are &ldquo;listening&rdquo; for pings from clients, and packet capturing them to get the IP addresses of users clients.
+
+```
+Genre               Name   IP:port
+
+Any Genre1          Duet   24.199.107.192:22121
+Any Genre2          Duet   24.199.107.192:22122
+Any Genre3          Duet   24.199.107.192:22123
+Rock                Duet   24.199.107.192:22124
+Jazz                Duet   24.199.107.192:22125
+Classical/Folk      Duet   24.199.107.192:22126
+Choral/Barbershop   Duet   24.199.107.192:22127
+```
+
+### User Data
+
+There is an explorer instance collecting lists of servers and users running from **`137.184.43.255`**  
+IP addresses of users collected from the listeners are being correlated with join events derived from the explorer instance to produce IP&lt;&dash;&gt;username mappings. IP addresses are processed to provide geolocation data of users. This geolocation data is being collected **and** displayed without express permission of users, and with no means to opt in or out.
+
+**This data is also being fed into AI for various analyses**, again with no express permission, and no means to opt in or out.
+
+## Mitigations
+
+### Clients
+
+When you open the Connect dialog window your client starts sending pings to every server in the list. **`24.199.107.192`** is the IP address of one of those servers. A server using **`24.199.107.192`** exists on each genre, their names are ***Duet***.
+
+Blocking outgoing **UDP** traffic on your DAW or router to **`24.199.107.192`** will prevent the listeners from collecting your IP address and break the correlation attack. This will help prevent you from being tracked.
+
+### Server Admins
+
+Server admins can contribute to helping prevent user tracking by blocking the explorer probe.  
+If you run a server on the jamulus public network, it is currently being indexed by the explorer instance on **`137.184.43.255`**
+
+Blocking incoming **UDP** traffic from **`137.184.43.255`** will prevent the explorer from indexing your server and breaks the correlation attack. This will protect users on your server from being tracked while they use it.
+
+---
+
+Updated information can be found here: [https://jamulusjams.com/block-user-tracking.html](https://jamulusjams.com/block-user-tracking.html)