From 21ce0229f4c19254cb6f5a0b3de8a3cd4f0c1897 Mon Sep 17 00:00:00 2001
From: Ben Davies <34197615+Kaiepi@users.noreply.github.com>
Date: Mon, 21 Oct 2019 07:17:49 -0300
Subject: [PATCH] Convert messages to Unicode NFKC in filter (#5905)

---
 server/chat-plugins/chat-monitor.js | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/server/chat-plugins/chat-monitor.js b/server/chat-plugins/chat-monitor.js
index 83516ba7aa..25f2a856f7 100644
--- a/server/chat-plugins/chat-monitor.js
+++ b/server/chat-plugins/chat-monitor.js
@@ -139,6 +139,12 @@ Chat.registerMonitor('evasion', {
 	punishment: 'EVASION',
 	label: 'Filter Evasion Detection',
 	monitor(line, room, user, message, lcMessage, isStaff) {
+		// Many codepoints used in filter evasion detection can be decomposed
+		// into multiple codepoints that are canonically equivalent to the
+		// original. Perform a canonical composition on the message to detect
+		// when people attempt to evade by abusing this behaviour of Unicode.
+		lcMessage = lcMessage.normalize('NFKC');
+
 		let [regex, word, reason] = line;
 		// Remove spaces and obvious false positives
 		lcMessage = lcMessage.replace(/[\s-_,.]/g, '');