diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..19eb735
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,6 @@
+# Sentinel's Journal
+
+## 2026-02-19 - Insecure Backup Permissions
+**Vulnerability:** Backup archives containing sensitive project data were created with default `umask` (often 022), making them readable by other users on the system (`-rw-rw-r--`).
+**Learning:** Even in single-user systems, assuming default permissions are secure is risky. Tools creating sensitive artifacts must explicitly enforce restrictive permissions.
+**Prevention:** Added `umask 077` to `tools/backup-projects.sh` and explicitly `chmod 700` on backup directories to ensure least privilege.
diff --git a/tests/verify_backup_permissions.sh b/tests/verify_backup_permissions.sh
new file mode 100755
index 0000000..5cbf019
--- /dev/null
+++ b/tests/verify_backup_permissions.sh
@@ -0,0 +1,99 @@
+#!/bin/bash
+set -e
+
+# Setup test environment
+# Use mktemp directory
+TEST_DIR=$(mktemp -d 2>/dev/null || mktemp -d -t 'test_backup')
+BACKUP_DIR="$TEST_DIR/backups"
+SOURCE_DIR="$TEST_DIR/source"
+CONFIG_FILE="$TEST_DIR/config.yaml"
+
+mkdir -p "$SOURCE_DIR"
+echo "secret" > "$SOURCE_DIR/secret.txt"
+
+# Create config file
+cat <<EOF > "$CONFIG_FILE"
+backup:
+  folders:
+    - "$SOURCE_DIR"
+  local:
+    base_dir: "$BACKUP_DIR"
+  remote:
+    enabled: false
+  logging:
+    enabled: false
+EOF
+
+# Determine repo root
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+BACKUP_SCRIPT="$REPO_ROOT/tools/backup-projects.sh"
+
+echo "Running backup script: $BACKUP_SCRIPT"
+# Run the backup command
+# We ignore output to reduce noise, but capture errors if needed
+bash "$BACKUP_SCRIPT" --config "$CONFIG_FILE" backup > "$TEST_DIR/backup.log" 2>&1 || {
+    echo "Backup script failed. Log:"
+    cat "$TEST_DIR/backup.log"
+    rm -rf "$TEST_DIR"
+    exit 1
+}
+
+# Check permissions
+BACKUP_ARCHIVE=$(find "$BACKUP_DIR" -name "*.zip" | head -n 1)
+
+if [[ ! -f "$BACKUP_ARCHIVE" ]]; then
+    echo "Backup failed: No archive created"
+    rm -rf "$TEST_DIR"
+    exit 1
+fi
+
+# Get permissions (Linux stat)
+if stat --version 2>/dev/null | grep -q "GNU"; then
+    # GNU stat
+    PERMS=$(stat -c "%a" "$BACKUP_ARCHIVE")
+    DIR_PERMS=$(stat -c "%a" "$BACKUP_DIR")
+elif stat --version 2>/dev/null; then
+     # Fallback for other stats that might support --version but not be GNU (unlikely)
+     PERMS=$(stat -c "%a" "$BACKUP_ARCHIVE")
+     DIR_PERMS=$(stat -c "%a" "$BACKUP_DIR")
+else
+    # BSD stat (macOS) - stat --version usually fails on BSD stat
+    # Try BSD syntax
+    if stat -f "%Lp" "$BACKUP_ARCHIVE" >/dev/null 2>&1; then
+        PERMS=$(stat -f "%Lp" "$BACKUP_ARCHIVE")
+        DIR_PERMS=$(stat -f "%Lp" "$BACKUP_DIR")
+    else
+        # Fallback to GNU syntax if --version check failed but it is GNU
+        PERMS=$(stat -c "%a" "$BACKUP_ARCHIVE")
+        DIR_PERMS=$(stat -c "%a" "$BACKUP_DIR")
+    fi
+fi
+
+echo "Backup Archive Permissions: $PERMS"
+echo "Backup Directory Permissions: $DIR_PERMS"
+
+FAILED=0
+
+# Check archive permissions (should be 600 or 400)
+if [[ "$PERMS" != "600" && "$PERMS" != "400" ]]; then
+    echo "FAIL: Insecure archive permissions ($PERMS). Expected 600 or 400."
+    FAILED=1
+else
+    echo "PASS: Archive permissions are secure."
+fi
+
+# Check directory permissions (should be 700)
+if [[ "$DIR_PERMS" != "700" ]]; then
+    echo "FAIL: Insecure directory permissions ($DIR_PERMS). Expected 700."
+    FAILED=1
+else
+    echo "PASS: Directory permissions are secure."
+fi
+
+rm -rf "$TEST_DIR"
+
+if [[ $FAILED -eq 1 ]]; then
+    exit 1
+fi
+
+exit 0
diff --git a/tools/backup-projects.sh b/tools/backup-projects.sh
index 1b7f6d2..00e2205 100755
--- a/tools/backup-projects.sh
+++ b/tools/backup-projects.sh
@@ -26,6 +26,7 @@
 
 # Pipestatus
 set -o pipefail
+umask 077 # Secure permissions for backups
 
 # --- Configuration ---
 CONFIG_FILE="${XDG_CONFIG_HOME:-$HOME/.config}/dotfiles/config.yaml"
@@ -351,7 +352,9 @@ cmd_backup() {
     # Setup directories
     if [[ "$DRY_RUN" != true ]]; then
         mkdir -p "$BACKUP_TEMP_DIR"
+        chmod 700 "$BACKUP_TEMP_DIR"
         mkdir -p "$LOG_DIR"
+        chmod 700 "$LOG_DIR"
     else
         debug "Would create: $BACKUP_TEMP_DIR"
         debug "Would create: $LOG_DIR"