diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8450923f..504698ba 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,7 +17,6 @@ Check the [documentation](https://johnxlivingston.github.io/peertube-plugin-live
 
 TODO: documentation, and settings names/descriptions changes related to direct XMPP S2S connections.
 TODO?: mod_s2s_peertubelivechat: dont allow to connect to remote server that are not Peertube servers?
-TODO: when sanitizing remote chat endpoint, check that the domain is the same as the video domain (or is room.videodomain.tld).
 TODO: only compatible with Prosody 0.12.x. So it should be documented for people using «system Prosody». And i should fix the ARM AppImage.
 TODO: it seems that in some case A->B can be Websocket, and B->A direct S2S. Check if this is fine. And maybe we can optimise some code, by allowing directS2S event if current server dont accept it.
 TODO?: always generate self-signed certificates. Could be used for outgoing s2s?
diff --git a/server/lib/federation/fetch-infos.ts b/server/lib/federation/fetch-infos.ts
index 2c405e11..1aae2144 100644
--- a/server/lib/federation/fetch-infos.ts
+++ b/server/lib/federation/fetch-infos.ts
@@ -80,7 +80,7 @@ async function fetchMissingRemoteServerInfos (
       return
     }
 
-    const serverInfos = sanitizePeertubeLiveChatServerInfos(options, response)
+    const serverInfos = sanitizePeertubeLiveChatServerInfos(options, response, remoteInstanceUrl)
     if (serverInfos) {
       await storeRemoteServerInfos(options, serverInfos)
     }
diff --git a/server/lib/federation/incoming.ts b/server/lib/federation/incoming.ts
index 404e3ee8..0f0276d4 100644
--- a/server/lib/federation/incoming.ts
+++ b/server/lib/federation/incoming.ts
@@ -16,7 +16,7 @@ async function readIncomingAPVideo (
   let peertubeLiveChat = ('peertubeLiveChat' in videoAPObject) ? videoAPObject.peertubeLiveChat : false
 
   // We must sanitize peertubeLiveChat, as it comes for the outer world.
-  peertubeLiveChat = sanitizePeertubeLiveChatInfos(options, peertubeLiveChat)
+  peertubeLiveChat = sanitizePeertubeLiveChatInfos(options, peertubeLiveChat, video.url)
 
   await storeVideoLiveChatInfos(options, video, peertubeLiveChat)
   if (video.remote) {
diff --git a/server/lib/federation/sanitize.ts b/server/lib/federation/sanitize.ts
index fa141c8c..350385fe 100644
--- a/server/lib/federation/sanitize.ts
+++ b/server/lib/federation/sanitize.ts
@@ -10,10 +10,16 @@ import { URL } from 'url'
  * This function can be used when informations are incoming,
  * or when reading stored information (to automatically migrate them)
  *
+ * @param options server options
  * @param chatInfos remote chat informations
+ * @param referenceUrl optional url string. If given, we must check that urls are on the same domain, to avoid spoofing.
  * @returns a sanitized version of the remote chat informations
  */
-function sanitizePeertubeLiveChatInfos (options: RegisterServerOptions, chatInfos: any): LiveChatJSONLDAttributeV1 {
+function sanitizePeertubeLiveChatInfos (
+  options: RegisterServerOptions,
+  chatInfos: any,
+  referenceUrl?: string
+): LiveChatJSONLDAttributeV1 {
   if (chatInfos === false) { return false }
   if (typeof chatInfos !== 'object') { return false }
 
@@ -22,13 +28,13 @@ function sanitizePeertubeLiveChatInfos (options: RegisterServerOptions, chatInfo
 
   if (!('xmppserver' in chatInfos)) {
     // V0 format, migrating on the fly to v1.
-    return _sanitizePeertubeLiveChatInfosV0(options, chatInfos)
+    return _sanitizePeertubeLiveChatInfosV0(options, chatInfos, referenceUrl)
   }
 
   if (!chatInfos.xmppserver || (typeof chatInfos.xmppserver !== 'object')) {
     return false
   }
-  const xmppserver = sanitizePeertubeLiveChatServerInfos(options, chatInfos.xmppserver)
+  const xmppserver = sanitizePeertubeLiveChatServerInfos(options, chatInfos.xmppserver, referenceUrl)
   if (!xmppserver) { return false }
 
   const r: LiveChatJSONLDAttributeV1 = {
@@ -40,18 +46,41 @@ function sanitizePeertubeLiveChatInfos (options: RegisterServerOptions, chatInfo
   return r
 }
 
+/**
+ * Use this function for incoming remote server informations.
+ * It will sanitize them, by checking everything is ok.
+ * It can also migrate from old format to the new one.
+ *
+ * This function can be used when informations are incoming,
+ * or when reading stored information (to automatically migrate them)
+ * @param options server options
+ * @param xmppserver remote server information
+ * @param referenceUrl optional url string. If given, we must check that urls are on the same domain, to avoid spoofing.
+ * @returns a sanitized version of remote server information (or false if not valid)
+ */
 function sanitizePeertubeLiveChatServerInfos (
-  options: RegisterServerOptions, xmppserver: any
+  options: RegisterServerOptions, xmppserver: any, referenceUrl?: string
 ): PeertubeXMPPServerInfos | false {
   if (!xmppserver || (typeof xmppserver !== 'object')) {
     return false
   }
 
+  let checkHost: undefined | string
+  if (referenceUrl) {
+    checkHost = _readReferenceUrl(referenceUrl)
+    if (!checkHost) {
+      options.peertubeHelpers.logger.error(
+        'sanitizePeertubeLiveChatServerInfos: got an invalid referenceUrl: ' + referenceUrl
+      )
+      return false
+    }
+  }
+
   if ((typeof xmppserver.host) !== 'string') { return false }
-  const host = _validateHost(xmppserver.host)
+  const host = _validateHost(xmppserver.host, checkHost)
   if (!host) { return false }
   if ((typeof xmppserver.muc) !== 'string') { return false }
-  const muc = _validateHost(xmppserver.muc)
+  const muc = _validateHost(xmppserver.muc, checkHost)
   if (!muc) { return false }
 
   const r: PeertubeXMPPServerInfos = {
@@ -74,7 +103,8 @@ function sanitizePeertubeLiveChatServerInfos (
       const url = xmppserver.websockets2s.url
       if ((typeof url === 'string') && _validUrl(url, {
         noSearchParams: true,
-        protocol: 'ws.'
+        protocol: 'ws.',
+        domain: checkHost
       })) {
         r.websockets2s = {
           url
@@ -83,7 +113,7 @@ function sanitizePeertubeLiveChatServerInfos (
     }
   }
   if (xmppserver.anonymous) {
-    const virtualhost = _validateHost(xmppserver.anonymous.virtualhost)
+    const virtualhost = _validateHost(xmppserver.anonymous.virtualhost, checkHost)
     if (virtualhost) {
       r.anonymous = {
         virtualhost
@@ -92,7 +122,8 @@ function sanitizePeertubeLiveChatServerInfos (
       const bosh = xmppserver.anonymous.bosh
       if ((typeof bosh === 'string') && _validUrl(bosh, {
         noSearchParams: true,
-        protocol: 'http.'
+        protocol: 'http.',
+        domain: checkHost
       })) {
         r.anonymous.bosh = bosh
       }
@@ -100,7 +131,8 @@ function sanitizePeertubeLiveChatServerInfos (
       const websocket = xmppserver.anonymous.websocket
       if ((typeof websocket === 'string') && _validUrl(websocket, {
         noSearchParams: true,
-        protocol: 'ws.'
+        protocol: 'ws.',
+        domain: checkHost
       })) {
         r.anonymous.websocket = websocket
       }
@@ -113,6 +145,7 @@ function sanitizePeertubeLiveChatServerInfos (
 interface URLConstraints {
   protocol: 'http.' | 'ws.'
   noSearchParams: boolean
+  domain?: string
 }
 
 function _validUrl (s: string, constraints: URLConstraints): boolean {
@@ -143,21 +176,57 @@ function _validUrl (s: string, constraints: URLConstraints): boolean {
     }
   }
 
+  if (constraints.domain) {
+    if (url.hostname !== constraints.domain) {
+      return false
+    }
+  }
+
   return true
 }
 
-function _validateHost (s: any): false | string {
+function _validateHost (s: any, mustBeSubDomainOf?: string): false | string {
   try {
     if (typeof s !== 'string') { return false }
     if (s.includes('/')) { return false }
     const url = new URL('http://' + s)
-    return url.hostname
+    const hostname = url.hostname
+    if (mustBeSubDomainOf && hostname !== mustBeSubDomainOf) {
+      const parts = hostname.split('.')
+      if (parts.length <= 2) {
+        return false
+      }
+      parts.shift()
+      if (parts.join('.') !== mustBeSubDomainOf) {
+        return false
+      }
+    }
+    return hostname
   } catch (_err) {
     return false
   }
 }
 
-function _sanitizePeertubeLiveChatInfosV0 (options: RegisterServerOptions, chatInfos: any): LiveChatJSONLDAttributeV1 {
+function _readReferenceUrl (s: any): undefined | string {
+  try {
+    if (typeof s !== 'string') { return undefined }
+    if (!s.startsWith('https://') && !s.startsWith('http://')) {
+      s = 'http://' + s
+    }
+    const url = new URL(s)
+    const host = url.hostname
+    // Just to avoid some basic spoofing, we must check that host is not simply something like "com".
+    // We will check if there is at least one dot. This test is not perfect, but can limit spoofing cases.
+    if (!host.includes('.')) { return undefined }
+    return host
+  } catch (_err) {
+    return undefined
+  }
+}
+
+function _sanitizePeertubeLiveChatInfosV0 (
+  options: RegisterServerOptions, chatInfos: any, referenceUrl?: string
+): LiveChatJSONLDAttributeV1 {
   const logger = options.peertubeHelpers.logger
   logger.debug('We are have to migrate data from the old JSONLD format')
 
@@ -170,13 +239,24 @@ function _sanitizePeertubeLiveChatInfosV0 (options: RegisterServerOptions, chatI
   // no link? invalid! dropping all.
   if (!Array.isArray(chatInfos.links)) { return false }
 
-  const muc = _validateHost(chatInfos.jid.split('@')[1])
+  let checkHost: undefined | string
+  if (referenceUrl) {
+    checkHost = _readReferenceUrl(referenceUrl)
+    if (!checkHost) {
+      options.peertubeHelpers.logger.error(
+        '_sanitizePeertubeLiveChatInfosV0: got an invalid referenceUrl: ' + referenceUrl
+      )
+      return false
+    }
+  }
+
+  const muc = _validateHost(chatInfos.jid.split('@')[1], checkHost)
   if (!muc) { return false }
   if (!muc.startsWith('room.')) {
     logger.error('We expected old format host to begin with "room.". Discarding.')
     return false
   }
-  const host = _validateHost(muc.replace(/^room\./, ''))
+  const host = _validateHost(muc.replace(/^room\./, ''), checkHost)
   if (!host) { return false }
 
   const r: LiveChatJSONLDAttributeV1 = {
@@ -197,7 +277,8 @@ function _sanitizePeertubeLiveChatInfosV0 (options: RegisterServerOptions, chatI
       if (
         !_validUrl(link.url, {
           noSearchParams: true,
-          protocol: link.type === 'xmpp-websocket-anonymous' ? 'ws.' : 'http.'
+          protocol: link.type === 'xmpp-websocket-anonymous' ? 'ws.' : 'http.',
+          domain: checkHost
         })
       ) {
         continue