fix: force download for untyped (octet-stream) served blobs

The /files handler served the application/octet-stream fallback with no
Content-Disposition, letting a browser render it inline — a stored-XSS vector if
the blob is crafted HTML/JS. Add Content-Disposition: attachment for that type
(belt to the existing nosniff); known image types stay inline.

Test (new tests/api_files.rs): octet-stream → attachment; png → inline.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/Cargo.lock

@@ -1558,7 +1558,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.128.8"
+version = "0.128.9"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.128.8"
+version = "0.128.9"
 edition = "2021"
 default-run = "mangalord"
 

backend/src/api/files.rs

@@ -141,7 +141,7 @@ fn image_response(
     content_length: String,
     body: Body,
 ) -> Response {
-    let headers = [
+    let mut headers = vec![
         (header::CONTENT_TYPE, content_type.to_string()),
         (header::CONTENT_LENGTH, content_length),
         // `nosniff` makes the contract explicit: the browser must trust the
@@ -169,7 +169,17 @@ fn image_response(
             },
         ),
     ];
-    (headers, body).into_response()
+    // Known image types render inline (covers/pages display in the reader). The
+    // `application/octet-stream` fallback is a blob we couldn't type — it could
+    // be crafted HTML/JS, so force a download rather than let the browser render
+    // it inline. Belt to `nosniff`'s braces.
+    if content_type == "application/octet-stream" {
+        headers.push((
+            header::CONTENT_DISPOSITION,
+            "attachment".to_string(),
+        ));
+    }
+    (axum::response::AppendHeaders(headers), body).into_response()
 }
 
 /// Parse and clamp a requested thumbnail width. Returns `None` for absent /

backend/tests/api_files.rs

@@ -0,0 +1,57 @@
+mod common;
+
+use axum::http::StatusCode;
+use tower::ServiceExt;
+
+/// Write a blob straight into the harness storage root at `key`, bypassing the
+/// upload handlers — the only way to land a key whose extension resolves to the
+/// `application/octet-stream` fallback (uploads always mint image extensions).
+fn write_blob(h: &common::Harness, key: &str, bytes: &[u8]) {
+    let path = h._storage_dir.path().join(key);
+    std::fs::create_dir_all(path.parent().unwrap()).unwrap();
+    std::fs::write(path, bytes).unwrap();
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn octet_stream_blobs_are_served_as_attachment(pool: sqlx::PgPool) {
+    // A blob with an unknown extension serves as application/octet-stream. Such a
+    // body could be crafted HTML/JS, so it must never render inline: force a
+    // download with Content-Disposition: attachment (nosniff is already set).
+    let h = common::harness(pool);
+    write_blob(&h, "misc/blob.bin", b"\x00\x01not-an-image");
+
+    let resp = h
+        .app
+        .oneshot(common::get("/api/v1/files/misc/blob.bin"))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+    assert_eq!(
+        resp.headers().get("content-type").unwrap(),
+        "application/octet-stream"
+    );
+    assert_eq!(
+        resp.headers().get("content-disposition").unwrap(),
+        "attachment"
+    );
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn image_blobs_are_served_inline(pool: sqlx::PgPool) {
+    // Regression guard: known image types keep rendering inline (no attachment
+    // disposition), so covers/pages still display in the reader.
+    let h = common::harness(pool);
+    write_blob(&h, "misc/pic.png", &common::fake_png_bytes());
+
+    let resp = h
+        .app
+        .oneshot(common::get("/api/v1/files/misc/pic.png"))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+    assert_eq!(resp.headers().get("content-type").unwrap(), "image/png");
+    assert!(
+        resp.headers().get("content-disposition").is_none(),
+        "images must render inline, not download"
+    );
+}