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feat: client-side ClamAV scanning for encrypted rooms (Issue #19)

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Synapse's own check_media_file_for_spam module can never see E2EE
attachment content - only the client ever holds the decryption key.
Adds two hooks that call a self-hosted scan service
(https://axion1337.chat/_scan, deployed separately in the gitops repo):

- DecryptFile.ts: scans every decrypted attachment (image/audio/video/
  file all funnel through this one function via MediaEventHelper)
  before returning it as a Blob.
- ContentMessages.ts: scans plaintext before encryption/upload in
  uploadFile(), the shared function behind all attachment uploads
  (main file, thumbnails, voice messages), regardless of room
  encryption state.

New ContentScanRejectedError surfaces through the existing error-
rendering paths (MediaProcessingError, upload failure dialog) using
the same pattern as DecryptError/DownloadError/UploadFailedError.

Live-tested: EICAR blocked pre-upload in encrypted rooms and DMs;
receive-side hook also blocks EICAR sent by an unpatched client
(app.element.io), confirming it isn't just self-protection for our
own uploads. Fails open on scanner errors so an outage can't block
all uploads/downloads.
This commit is contained in:
Thore Cimbal
2026-07-29 12:00:00 +00:00
parent 44305556c3
commit 42285021cb
8 changed files with 134 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files
apps/web/src/ContentMessages.ts
+21 -2
View File
@@ -49,6 +49,7 @@ import SettingsStore from "./settings/SettingsStore";
import { decorateStartSendingTime, sendRoundTripMetric } from "./sendTimePerformanceMetrics";
import { TimelineRenderingType } from "./contexts/RoomContext";
import { addReplyToMessageContent } from "./utils/Reply";
import { scanContent, ContentScanRejectedError } from "./utils/ContentScanner";
import ErrorDialog from "./components/views/dialogs/ErrorDialog";
import UploadFailureDialog from "./components/views/dialogs/UploadFailureDialog";
import UploadConfirmDialog from "./components/views/dialogs/UploadConfirmDialog";
@@ -350,10 +351,24 @@ export async function uploadFile(
): Promise<{ url?: string; file?: EncryptedFile }> {
const abortController = controller ?? new AbortController();
// Issue #19 extension: scan the plaintext before it's ever encrypted or uploaded - the
// one place both directions of client-side scanning meet, since this function backs
// every room-attachment upload (main file, generated thumbnails, and voice messages -
// see VoiceMessageRecording.ts) regardless of whether the target room is encrypted.
// This does mean reading the whole file into memory even for unencrypted-room uploads,
// which previously streamed straight from the File object - unavoidable, since scanning
// requires the bytes in hand either way.
const dataForScan = await readFileAsArrayBuffer(file);
if (abortController.signal.aborted) throw new UploadCanceledError();
const accessTokenForScan = matrixClient.getAccessToken();
if (accessTokenForScan) {
await scanContent(dataForScan, accessTokenForScan);
}
// If the room is encrypted then encrypt the file before uploading it.
if (await matrixClient.getCrypto()?.isEncryptionEnabledInRoom(roomId)) {
// First read the file into memory.
const data = await readFileAsArrayBuffer(file);
// Already read into memory above (dataForScan).
const data = dataForScan;
if (abortController.signal.aborted) throw new UploadCanceledError();
// Then encrypt the file.
@@ -670,6 +685,10 @@ export default class ContentMessages {
desc = _t("upload_failed_size", {
fileName: upload.fileName,
});
} else if (unwrappedError instanceof ContentScanRejectedError) {
desc = _t("upload_failed_scan_rejected", {
fileName: upload.fileName,
});
}
Modal.createDialog(ErrorDialog, {
title: _t("upload_failed_title"),
apps/web/src/components/views/messages/MAudioBody.tsx
+9 -8
View File
@@ -21,9 +21,10 @@ import RoomContext, { TimelineRenderingType } from "../../../contexts/RoomContex
import MediaProcessingError from "./shared/MediaProcessingError";
import { AudioPlayerViewModel } from "../../../viewmodels/room/timeline/event-tile/body/AudioPlayerViewModel";
import { FileBodyFactory, renderMBody } from "./MBodyFactory";
import { ContentScanRejectedError } from "../../../utils/ContentScanner";
interface IState {
error?: boolean;
error?: unknown;
playback?: Playback;
}
@@ -40,12 +41,12 @@ export default class MAudioBody extends React.PureComponent<IBodyProps, IState>
const blob = await this.props.mediaEventHelper!.sourceBlob.value;
buffer = await blob.arrayBuffer();
} catch (e) {
this.setState({ error: true });
this.setState({ error: e });
logger.warn("Unable to decrypt audio message", e);
return; // stop processing the audio file
}
} catch (e) {
this.setState({ error: true });
this.setState({ error: e });
logger.warn("Unable to decrypt/download audio message", e);
return; // stop processing the audio file
}
@@ -81,11 +82,11 @@ export default class MAudioBody extends React.PureComponent<IBodyProps, IState>
public render(): React.ReactNode {
if (this.state.error) {
return (
<MediaProcessingError className="mx_MAudioBody">
{_t("timeline|m.audio|error_processing_audio")}
</MediaProcessingError>
);
const errorText =
this.state.error instanceof ContentScanRejectedError
? _t("timeline|m.audio|error_scan_rejected")
: _t("timeline|m.audio|error_processing_audio");
return <MediaProcessingError className="mx_MAudioBody">{errorText}</MediaProcessingError>;
}
if (this.props.forExport) {
apps/web/src/components/views/messages/MImageBody.tsx
+3
View File
@@ -34,6 +34,7 @@ import { presentableTextForFile } from "../../../utils/FileUtils";
import { createReconnectedListener } from "../../../utils/connection";
import MediaProcessingError from "./shared/MediaProcessingError";
import { DecryptError, DownloadError } from "../../../utils/DecryptFile";
import { ContentScanRejectedError } from "../../../utils/ContentScanner";
import { useMediaVisible } from "../../../hooks/useMediaVisible";
import { isMimeTypeAllowed } from "../../../utils/blobs.ts";
import { FileBodyFactory, renderMBody } from "./MBodyFactory";
@@ -673,6 +674,8 @@ export class MImageBodyInner extends React.Component<IProps, IState> {
errorText = _t("timeline|m.image|error_decrypting");
} else if (this.state.error instanceof DownloadError) {
errorText = _t("timeline|m.image|error_downloading");
} else if (this.state.error instanceof ContentScanRejectedError) {
errorText = _t("timeline|m.image|error_scan_rejected");
}
return (
apps/web/src/i18n/strings/en_EN.json
+7 -2
View File
@@ -3400,7 +3400,8 @@
"m.audio": {
"error_downloading_audio": "Error downloading audio",
"error_processing_audio": "Error processing audio message",
"error_processing_voice_message": "Error processing voice message"
"error_processing_voice_message": "Error processing voice message",
"error_scan_rejected": "This audio was blocked by the content scanner"
},
"m.beacon_info": {
"view_live_location": "View live location"
@@ -3432,12 +3433,14 @@
"voice_call_unsupported": "%(senderName)s placed a voice call. (not supported by this browser)"
},
"m.file": {
"error_decrypting": "Error decrypting attachment"
"error_decrypting": "Error decrypting attachment",
"error_scan_rejected": "This file was blocked by the content scanner"
},
"m.image": {
"error": "Unable to show image due to error",
"error_decrypting": "Error decrypting image",
"error_downloading": "Error downloading image",
"error_scan_rejected": "This image was blocked by the content scanner",
"sent": "%(senderDisplayName)s sent an image.",
"show_image": "Show image"
},
@@ -3563,6 +3566,7 @@
"m.sticker": "%(senderDisplayName)s sent a sticker.",
"m.video": {
"error_decrypting": "Error decrypting video",
"error_scan_rejected": "This video was blocked by the content scanner",
"show_video": "Show video"
},
"m.widget": {
@@ -3805,6 +3809,7 @@
"title": "Allow guest users to join this room"
},
"upload_failed_generic": "The file '%(fileName)s' failed to upload.",
"upload_failed_scan_rejected": "The file '%(fileName)s' was blocked by the content scanner.",
"upload_failed_size": "The file '%(fileName)s' exceeds this homeserver's size limit for uploads",
"upload_failed_title": "Upload Failed",
"upload_file": {
apps/web/src/utils/ContentScanner.ts
+63
View File
@@ -0,0 +1,63 @@
/*
Copyright 2026 aXion1337
SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
Please see LICENSE files in the repository root for full details.
*/
// Client-side ClamAV scanning (Issue #19 extension): Synapse's own server-side spam-checker
// module can never see E2EE attachment content - only a cooperating client can, since only
// the client ever holds the room's decryption key. This calls a small self-hosted scan
// service (same ClamAV instance the server-side module uses) directly from the browser, both
// before encrypting/uploading a file and after downloading/decrypting one - see
// ContentMessages.ts (send) and DecryptFile.ts (receive) for the two call sites.
import { logger } from "matrix-js-sdk/src/logger";
export class ContentScanRejectedError extends Error {
public readonly signature: string;
public constructor(signature: string) {
super(`Blocked by content scanner: ${signature}`);
this.name = "ContentScanRejectedError";
this.signature = signature;
}
}
/**
* Scans plaintext bytes against the self-hosted ClamAV scan service.
* Fails open (resolves normally) on any network/scanner-side error, matching the same
* fail-open policy as the server-side Synapse module - a scanner outage should not block
* uploads or downloads site-wide.
* @throws {ContentScanRejectedError} if the scanner positively identifies the content as infected.
*/
export async function scanContent(data: ArrayBuffer | ArrayBufferView, accessToken: string): Promise<void> {
let response: Response;
try {
response = await fetch("/_scan", {
method: "POST",
headers: { Authorization: `Bearer ${accessToken}` },
body: data as BodyInit,
});
} catch (e) {
logger.warn("Content scan request failed (scanner unreachable?) - allowing through", e);
return;
}
if (!response.ok) {
logger.warn("Content scan request failed with status", response.status, "- allowing through");
return;
}
let result: { clean: boolean; signature?: string };
try {
result = await response.json();
} catch (e) {
logger.warn("Content scan response was not valid JSON - allowing through", e);
return;
}
if (result.clean === false) {
throw new ContentScanRejectedError(result.signature ?? "unknown");
}
}
apps/web/src/utils/DecryptFile.ts
+21 -5
View File
@@ -13,6 +13,8 @@ import { type EncryptedFile, type MediaEventInfo } from "matrix-js-sdk/src/types
import { mediaFromContent } from "../customisations/Media";
import { getBlobSafeMimeType } from "./blobs";
import { MatrixClientPeg } from "../MatrixClientPeg";
import { scanContent, ContentScanRejectedError } from "./ContentScanner";
export class DownloadError extends Error {
public constructor(e: Error) {
@@ -30,6 +32,8 @@ export class DecryptError extends Error {
}
}
export { ContentScanRejectedError };
/**
* Decrypt a file attached to a matrix event.
* @param {EncryptedFile} file The encrypted file information taken from the matrix event.
@@ -55,19 +59,31 @@ export async function decryptFile(file?: EncryptedFile, info?: MediaEventInfo):
throw new DownloadError(e as Error);
}
let dataArray: ArrayBuffer;
let mimetype: string;
try {
// Decrypt the array buffer using the information taken from the event content.
const dataArray = await encrypt.decryptAttachment(responseData, file!);
// Turn the array into a Blob and give it the correct MIME-type.
dataArray = await encrypt.decryptAttachment(responseData, file!);
// IMPORTANT: we must not allow scriptable mime-types into Blobs otherwise
// they introduce XSS attacks if the Blob URI is viewed directly in the
// browser (e.g. by copying the URI into a new tab or window.)
// See warning at top of file.
const mimetype = getBlobSafeMimeType(info?.mimetype?.split(";")[0].trim() ?? "");
return new Blob([dataArray], { type: mimetype });
mimetype = getBlobSafeMimeType(info?.mimetype?.split(";")[0].trim() ?? "");
} catch (e) {
throw new DecryptError(e as Error);
}
// Issue #19 extension: Synapse's own media scanner never sees this content (it's
// ciphertext to the server) - this is the one place in the whole app where decrypted
// plaintext for *every* attachment type first exists, so scanning here covers all of
// them in one spot. Deliberately outside the try/catch above: a scan rejection is a
// distinct outcome from a decrypt failure, not wrapped as a DecryptError.
const accessToken = MatrixClientPeg.safeGet()?.getAccessToken();
if (accessToken) {
await scanContent(dataArray, accessToken);
}
// Turn the array into a Blob and give it the correct MIME-type.
return new Blob([dataArray], { type: mimetype });
}
apps/web/src/viewmodels/message-body/FileBodyViewModel.ts
+5 -1
View File
@@ -25,6 +25,7 @@ import { FileDownloader } from "../../utils/FileDownloader";
import { type MediaEventHelper } from "../../utils/MediaEventHelper";
import { TimelineRenderingType } from "../../contexts/RoomContext";
import ErrorDialog from "../../components/views/dialogs/ErrorDialog";
import { ContentScanRejectedError } from "../../utils/ContentScanner";
export interface FileBodyViewModelProps {
mxEvent: MatrixEvent;
@@ -249,7 +250,10 @@ export class FileBodyViewModel
logger.warn("Unable to decrypt attachment: ", err);
Modal.createDialog(ErrorDialog, {
title: _t("common|error"),
description: _t("timeline|m.file|error_decrypting"),
description:
err instanceof ContentScanRejectedError
? _t("timeline|m.file|error_scan_rejected")
: _t("timeline|m.file|error_decrypting"),
});
}
};
apps/web/src/viewmodels/message-body/VideoBodyViewModel.ts
+5 -1
View File
@@ -23,6 +23,7 @@ import { mediaFromContent } from "../../customisations/Media";
import { BLURHASH_FIELD } from "../../utils/image-media";
import { type ImageSize, suggestedSize as suggestedVideoSize } from "../../settings/enums/ImageSize";
import { type MediaEventHelper } from "../../utils/MediaEventHelper";
import { ContentScanRejectedError } from "../../utils/ContentScanner";
export interface VideoBodyViewModelProps {
/**
@@ -203,7 +204,10 @@ export class VideoBodyViewModel
if (state.error !== null) {
return {
state: VideoBodyViewState.ERROR,
errorLabel: _t("timeline|m.video|error_decrypting"),
errorLabel:
state.error instanceof ContentScanRejectedError
? _t("timeline|m.video|error_scan_rejected")
: _t("timeline|m.video|error_decrypting"),
maxWidth,
maxHeight,
aspectRatio,