From 8a9d3071778eb146109ae6ee7fc09daabe706fd1 Mon Sep 17 00:00:00 2001
From: Gustavo Madeira Santana <gumadeiras@gmail.com>
Date: Thu, 12 Mar 2026 08:51:26 +0000
Subject: [PATCH] Matrix: avoid alias trust in group context

---
 .../matrix/src/matrix/monitor/handler.test.ts | 38 +++++++++++++++++++
 .../matrix/src/matrix/monitor/handler.ts      | 26 ++++++++++---
 2 files changed, 58 insertions(+), 6 deletions(-)

diff --git a/extensions/matrix/src/matrix/monitor/handler.test.ts b/extensions/matrix/src/matrix/monitor/handler.test.ts
index 50c4ecbd9bb..45add7bbbe2 100644
--- a/extensions/matrix/src/matrix/monitor/handler.test.ts
+++ b/extensions/matrix/src/matrix/monitor/handler.test.ts
@@ -256,6 +256,7 @@ describe("matrix monitor handler pairing account scope", () => {
   it("skips media downloads for unmentioned group media messages", async () => {
     const downloadContent = vi.fn(async () => Buffer.from("image"));
     const getMemberDisplayName = vi.fn(async () => "sender");
+    const getRoomInfo = vi.fn(async () => ({ altAliases: [] }));
     const { handler, resolveAgentRoute } = createMatrixHandlerTestHarness({
       client: {
         downloadContent,
@@ -263,6 +264,7 @@ describe("matrix monitor handler pairing account scope", () => {
       isDirectMessage: false,
       mentionRegexes: [/@bot/i],
       getMemberDisplayName,
+      getRoomInfo,
     });
 
     await handler("!room:example.org", {
@@ -283,6 +285,7 @@ describe("matrix monitor handler pairing account scope", () => {
 
     expect(downloadContent).not.toHaveBeenCalled();
     expect(getMemberDisplayName).not.toHaveBeenCalled();
+    expect(getRoomInfo).not.toHaveBeenCalled();
     expect(resolveAgentRoute).not.toHaveBeenCalled();
   });
 
@@ -307,6 +310,7 @@ describe("matrix monitor handler pairing account scope", () => {
       prevBatch: null,
     }));
     const getMemberDisplayName = vi.fn(async () => "sender");
+    const getRoomInfo = vi.fn(async () => ({ altAliases: [] }));
     const { handler, resolveAgentRoute } = createMatrixHandlerTestHarness({
       client: {
         getEvent,
@@ -315,6 +319,7 @@ describe("matrix monitor handler pairing account scope", () => {
       isDirectMessage: false,
       mentionRegexes: [/@bot/i],
       getMemberDisplayName,
+      getRoomInfo,
     });
 
     await handler("!room:example.org", {
@@ -336,6 +341,7 @@ describe("matrix monitor handler pairing account scope", () => {
     expect(getEvent).not.toHaveBeenCalled();
     expect(getRelations).not.toHaveBeenCalled();
     expect(getMemberDisplayName).not.toHaveBeenCalled();
+    expect(getRoomInfo).not.toHaveBeenCalled();
     expect(resolveAgentRoute).not.toHaveBeenCalled();
   });
 
@@ -382,6 +388,38 @@ describe("matrix monitor handler pairing account scope", () => {
     );
   });
 
+  it("uses stable room ids instead of room-declared aliases in group context", async () => {
+    const { handler, finalizeInboundContext } = createMatrixHandlerTestHarness({
+      isDirectMessage: false,
+      getRoomInfo: async () => ({
+        name: "Ops Room",
+        canonicalAlias: "#spoofed:example.org",
+        altAliases: ["#alt:example.org"],
+      }),
+      getMemberDisplayName: async () => "sender",
+      dispatchReplyFromConfig: async () => ({
+        queuedFinal: false,
+        counts: { final: 0, block: 0, tool: 0 },
+      }),
+    });
+
+    await handler(
+      "!room:example.org",
+      createMatrixTextMessageEvent({
+        eventId: "$group1",
+        body: "@room hello",
+        mentions: { room: true },
+      }),
+    );
+
+    expect(finalizeInboundContext).toHaveBeenCalledWith(
+      expect.objectContaining({
+        GroupSubject: "Ops Room",
+        GroupChannel: "!room:example.org",
+      }),
+    );
+  });
+
   it("routes bound Matrix threads to the target session key", async () => {
     registerSessionBindingAdapter({
       channel: "matrix",
diff --git a/extensions/matrix/src/matrix/monitor/handler.ts b/extensions/matrix/src/matrix/monitor/handler.ts
index 8b052956772..c73272660b7 100644
--- a/extensions/matrix/src/matrix/monitor/handler.ts
+++ b/extensions/matrix/src/matrix/monitor/handler.ts
@@ -225,10 +225,6 @@ export function createMatrixRoomMessageHandler(params: MatrixMonitorHandlerParam
         return;
       }
 
-      const roomInfo = await getRoomInfo(roomId);
-      const roomName = roomInfo.name;
-      const roomAliases = [roomInfo.canonicalAlias ?? "", ...roomInfo.altAliases].filter(Boolean);
-
       let content = event.content as RoomMessageEventContent;
 
       if (
@@ -260,16 +256,32 @@ export function createMatrixRoomMessageHandler(params: MatrixMonitorHandlerParam
         selfUserId,
       });
       const isRoom = !isDirectMessage;
+      let roomInfoPromise: Promise<{
+        name?: string;
+        canonicalAlias?: string;
+        altAliases: string[];
+      }> | null = null;
+      const getResolvedRoomInfo = async () => {
+        roomInfoPromise ??= getRoomInfo(roomId);
+        return await roomInfoPromise;
+      };
 
       if (isRoom && groupPolicy === "disabled") {
         return;
       }
 
+      const roomInfoForConfig =
+        isRoom && roomsConfig && Object.keys(roomsConfig).some((key) => key.trim().startsWith("#"))
+          ? await getResolvedRoomInfo()
+          : undefined;
+      const roomAliasesForConfig = roomInfoForConfig
+        ? [roomInfoForConfig.canonicalAlias ?? "", ...roomInfoForConfig.altAliases].filter(Boolean)
+        : [];
       const roomConfigInfo = isRoom
         ? resolveMatrixRoomConfig({
             rooms: roomsConfig,
             roomId,
-            aliases: roomAliases,
+            aliases: roomAliasesForConfig,
           })
         : undefined;
       const roomConfig = roomConfigInfo?.config;
@@ -548,6 +560,8 @@ export function createMatrixRoomMessageHandler(params: MatrixMonitorHandlerParam
         return;
       }
       const senderName = await getSenderName();
+      const roomInfo = isRoom ? await getResolvedRoomInfo() : undefined;
+      const roomName = roomInfo?.name;
 
       const messageId = event.event_id ?? "";
       const replyToEventId = content["m.relates_to"]?.["m.in_reply_to"]?.event_id;
@@ -622,7 +636,7 @@ export function createMatrixRoomMessageHandler(params: MatrixMonitorHandlerParam
         SenderId: senderId,
         SenderUsername: senderId.split(":")[0]?.replace(/^@/, ""),
         GroupSubject: isRoom ? (roomName ?? roomId) : undefined,
-        GroupChannel: isRoom ? (roomInfo.canonicalAlias ?? roomId) : undefined,
+        GroupChannel: isRoom ? roomId : undefined,
         GroupSystemPrompt: isRoom ? groupSystemPrompt : undefined,
         Provider: "matrix" as const,
         Surface: "matrix" as const,