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

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.
2026-07-29 12:00:00 +00:00
parent 44305556c3
commit 42285021cb
8 changed files with 134 additions and 19 deletions
@@ -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");
+    }
+}