From 0e48014d5a7a8a584cf007b3c3017e0fa43c9976 Mon Sep 17 00:00:00 2001
From: Reto Brunner <reto@slightlybroken.com>
Date: Thu, 9 May 2024 17:41:12 +0200
Subject: [PATCH] ident: only respond if the ip,port tuples match

Per RFC 1413, The uniquely identifying tuple includes not only the ports,
but also both addresses.

If multiple connections happen to use the same local port number
(which is possible if the addresses differ), the username of the first
is returned for all, resulting in the wrong ident for all but the
first.

By not checking the connection address, the information becomes
public. Because there is only relatively small number of local ports,
and the remote ports are likely to be either 6667 or 6697, it becomes
trivial to enumerate all the users.

Co-Authored-By: Juerd Waalboer <juerd@tnx.nl>
---
 server/identification.ts | 42 ++++++++++++++++++++++++++++++++++------
 1 file changed, 36 insertions(+), 6 deletions(-)

diff --git a/server/identification.ts b/server/identification.ts
index 96648083..44dff894 100644
--- a/server/identification.ts
+++ b/server/identification.ts
@@ -73,24 +73,41 @@ class Identification {
 	}
 
 	respondToIdent(socket: Socket, buffer: Buffer) {
+		if (!socket.remoteAddress) {
+			log.warn("identd: no remote address");
+			return;
+		}
+
 		const data = buffer.toString().split(",");
 
 		const lport = parseInt(data[0], 10) || 0;
 		const fport = parseInt(data[1], 10) || 0;
 
 		if (lport < 1 || fport < 1 || lport > 65535 || fport > 65535) {
+			log.warn(`identd: bogus request from ${socket.remoteAddress}`);
 			return;
 		}
 
+		log.debug(`identd: remote ${socket.remoteAddress} query ${lport}, ${fport}`);
+
 		for (const connection of this.connections.values()) {
-			if (connection.socket.remotePort === fport && connection.socket.localPort === lport) {
-				return socket.write(
-					`${lport}, ${fport} : USERID : TheLounge : ${connection.user}\r\n`
-				);
+			// we only want to respond if all the ip,port tuples match, to avoid user enumeration
+			if (
+				connection.socket.remotePort === fport &&
+				connection.socket.localPort === lport &&
+				socket.remoteAddress === connection.socket.remoteAddress &&
+				socket.localAddress === connection.socket.localAddress
+			) {
+				const reply = `${lport}, ${fport} : USERID : TheLounge : ${connection.user}\r\n`;
+				log.debug(`identd: reply is ${reply.trimEnd()}`);
+				socket.write(reply);
+				return;
 			}
 		}
 
-		socket.write(`${lport}, ${fport} : ERROR : NO-USER\r\n`);
+		const reply = `${lport}, ${fport} : ERROR : NO-USER\r\n`;
+		log.debug(`identd: reply is ${reply.trimEnd()}`);
+		socket.write(reply);
 	}
 
 	addSocket(socket: Socket, user: string) {
@@ -127,8 +144,21 @@ class Identification {
 				return;
 			}
 
+			if (!connection.socket.remoteAddress) {
+				log.warn(`oidentd: socket has no remote address, will not respond to queries`);
+				return;
+			}
+
+			if (!connection.socket.localAddress) {
+				log.warn(`oidentd: socket has no local address, will not respond to queries`);
+				return;
+			}
+
+			// we only want to respond if all the ip,port tuples match, to avoid user enumeration
 			file +=
-				`fport ${connection.socket.remotePort}` +
+				`to ${connection.socket.remoteAddress}` +
+				` fport ${connection.socket.remotePort}` +
+				` from ${connection.socket.localAddress}` +
 				` lport ${connection.socket.localPort}` +
 				` { reply "${connection.user}" }\n`;
 		});