diff --git a/src-tauri/src/cloud_transfer.rs b/src-tauri/src/cloud_transfer.rs
index e5fc42665..f1c695786 100644
--- a/src-tauri/src/cloud_transfer.rs
+++ b/src-tauri/src/cloud_transfer.rs
@@ -1138,14 +1138,26 @@ fn write_immutable_receipt(
     if !directory_metadata.is_dir() || directory_metadata.file_type().is_symlink() {
         return Err("receipt-directory-unsafe".into());
     }
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::PermissionsExt;
+        if directory_metadata.permissions().mode() & 0o022 != 0 {
+            return Err("receipt-directory-writable-by-others".into());
+        }
+    }
     let path = receipt_dir.join(format!("{}.json", receipt.receipt_id));
     let encoded = serde_json::to_vec_pretty(receipt).map_err(|error| error.to_string())?;
     if encoded.len() as u64 > MAX_RECEIPT_BYTES {
         return Err("receipt-too-large".into());
     }
-    let mut file = std::fs::OpenOptions::new()
-        .write(true)
-        .create_new(true)
+    let mut options = std::fs::OpenOptions::new();
+    options.write(true).create_new(true);
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::OpenOptionsExt;
+        options.mode(0o400);
+    }
+    let mut file = options
         .open(&path)
         .map_err(|error| error.to_string())?;
     let result = (|| -> Result<(), String> {
@@ -1163,7 +1175,8 @@ fn write_immutable_receipt(
         }
         #[cfg(not(unix))]
         permissions.set_readonly(true);
-        std::fs::set_permissions(&path, permissions).map_err(|error| error.to_string())?;
+        file.set_permissions(permissions)
+            .map_err(|error| error.to_string())?;
         #[cfg(unix)]
         std::fs::File::open(receipt_dir)
             .and_then(|directory| directory.sync_all())
diff --git a/src-tauri/tests/cloud_receipt_private_authority.rs b/src-tauri/tests/cloud_receipt_private_authority.rs
new file mode 100644
index 000000000..855ace770
--- /dev/null
+++ b/src-tauri/tests/cloud_receipt_private_authority.rs
@@ -0,0 +1,149 @@
+#![cfg(unix)]
+
+use disksage_lib::cloud::{
+    candidate_review_fingerprint, ArchiveKind, CloudAccountScope, CloudCandidate, CloudProvider,
+    CloudRoot, MetadataEvidence,
+};
+use disksage_lib::cloud_transfer::{
+    cloud_copy_approval_phrase, create_cloud_copy_approval, prepare_cloud_copy_with_approval,
+    CloudCopyApprovalAction,
+};
+use std::os::unix::fs::PermissionsExt;
+
+fn now_ms() -> u64 {
+    std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .unwrap()
+        .as_millis() as u64
+}
+
+fn candidate_and_root(
+    temp: &tempfile::TempDir,
+) -> (CloudCandidate, CloudRoot, std::path::PathBuf) {
+    let source_dir = temp.path().join("source");
+    let cloud_dir = temp.path().join("cloud");
+    std::fs::create_dir_all(&source_dir).unwrap();
+    std::fs::create_dir_all(&cloud_dir).unwrap();
+
+    let source = source_dir.join("report.bin");
+    let destination = cloud_dir.join("report.bin");
+    std::fs::write(&source, b"verified source bytes").unwrap();
+    let metadata = std::fs::metadata(&source).unwrap();
+    let modified_ms = metadata
+        .modified()
+        .unwrap()
+        .duration_since(std::time::UNIX_EPOCH)
+        .unwrap()
+        .as_millis() as u64;
+
+    let mut candidate = CloudCandidate {
+        metadata_fingerprint: "a".repeat(64),
+        review_fingerprint: String::new(),
+        src: source.to_string_lossy().into_owned(),
+        dst: destination.to_string_lossy().into_owned(),
+        provider: CloudProvider::Onedrive,
+        destination_account_scope: CloudAccountScope::Personal,
+        kind: ArchiveKind::Document,
+        bytes: metadata.len(),
+        age_days: 1,
+        created_ms: modified_ms,
+        modified_ms,
+        production_time_ms: modified_ms,
+        production_time_source: "embedded:test:CreateDate".into(),
+        production_time_confidence: "high".into(),
+        source_root: source_dir.to_string_lossy().into_owned(),
+        relative_path: "report.bin".into(),
+        source_context: ".".into(),
+        requires_review: false,
+        review_reasons: Vec::new(),
+        content_title: Some("Report".into()),
+        content_authors: Vec::new(),
+        content_context: Vec::new(),
+        duration_ms: None,
+        dataset_profile: None,
+        metadata_evidence: vec![MetadataEvidence {
+            field: "production-date".into(),
+            value: "2026-08-12".into(),
+            source: "embedded:test:CreateDate".into(),
+            confidence: "high".into(),
+        }],
+        blocked_reason: None,
+    };
+    candidate.review_fingerprint = candidate_review_fingerprint(&candidate);
+
+    let root = CloudRoot {
+        id: cloud_dir.to_string_lossy().into_owned(),
+        provider: CloudProvider::Onedrive,
+        account_scope: CloudAccountScope::Personal,
+        label: "test".into(),
+        path: cloud_dir.to_string_lossy().into_owned(),
+        readable: true,
+        access_issue: None,
+    };
+    (candidate, root, destination)
+}
+
+#[test]
+fn shared_writable_receipt_directory_fails_closed_without_durable_authority() {
+    for unsafe_write_bit in [0o020, 0o002] {
+        let temp = tempfile::tempdir().unwrap();
+        let (candidate, root, destination) = candidate_and_root(&temp);
+        let receipt_dir = temp.path().join("receipts");
+        std::fs::create_dir_all(&receipt_dir).unwrap();
+        std::fs::set_permissions(
+            &receipt_dir,
+            std::fs::Permissions::from_mode(0o700 | unsafe_write_bit),
+        )
+        .unwrap();
+
+        let action = CloudCopyApprovalAction::CopyOnly;
+        let approval = create_cloud_copy_approval(
+            &candidate,
+            &root,
+            action,
+            now_ms(),
+            "human:local:test",
+            "authorize exact test cloud copy",
+            &cloud_copy_approval_phrase(&candidate, action),
+        )
+        .unwrap();
+
+        let error = prepare_cloud_copy_with_approval(
+            &candidate,
+            &root,
+            &receipt_dir,
+            None,
+            &approval,
+        )
+        .expect_err("shared-writable receipt authority must fail closed");
+
+        assert_eq!(error, "receipt-directory-writable-by-others");
+        assert!(std::path::Path::new(&candidate.src).exists());
+        assert!(
+            !destination.exists(),
+            "failed receipt publication must roll back the new copy"
+        );
+        assert_eq!(std::fs::read_dir(&receipt_dir).unwrap().count(), 0);
+    }
+}
+
+#[test]
+fn receipt_file_is_private_from_creation_and_object_bound_for_hardening() {
+    let source = std::fs::read_to_string(
+        std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("src/cloud_transfer.rs"),
+    )
+    .expect("cloud transfer source must be readable");
+
+    assert!(
+        source.contains("options.mode(0o400);"),
+        "cloud copy receipts must be owner-read-only from create_new so a crash cannot leave broader authority"
+    );
+    assert!(
+        source.contains("file.set_permissions(permissions)"),
+        "post-write receipt hardening must remain bound to the opened file object"
+    );
+    assert!(
+        !source.contains("std::fs::set_permissions(&path, permissions)"),
+        "receipt hardening must not re-resolve a replaceable pathname after create_new"
+    );
+}