--- last_modified: 2026-05-21 title: "Permissions" description: "Reference for Deno's permission system: how the runtime sandbox works and how to grant or deny file system, network, environment, system, subprocess, FFI, and import access with the --allow and --deny flags." oldUrl: - /runtime/manual/basics/permissionsDeno/ - /manual/basics/permissions - /runtime/manual/basics/permissions - /runtime/manual/getting_started/permissions --- Deno runs code in a secure sandbox: a program has no access to sensitive system I/O unless you grant it. This page is the reference for every permission and the `--allow-*` / `--deny-*` flags that control it. For the security model behind it and guidance on running untrusted code, see [Security](/runtime/fundamentals/security/). By default, access to most system I/O is denied. There are some I/O operations that are allowed in a limited capacity, even by default. These are described below. To enable these operations, the user must explicitly grant permission to the Deno runtime. This is done by passing the `--allow-read`, `--allow-write`, `--allow-net`, `--allow-env`, and `--allow-run` flags to the `deno` command. During execution of a script, a user can also explicitly grant permission to specific files, directories, network addresses, environment variables, and subprocesses when prompted by the runtime. Prompts are not shown if stdout/stderr are not a TTY, or when the `--no-prompt` flag is passed to the `deno` command. Users can also explicitly disallow access to specific resources by using the `--deny-read`, `--deny-write`, `--deny-net`, `--deny-env`, and `--deny-run` flags. These flags take precedence over the allow flags. For example, if you allow network access but deny access to a specific domain, the deny flag will take precedence. Deno also provides a `--allow-all` flag that grants all permissions to the script. This **disables** the security sandbox entirely, and should be used with caution. The `--allow-all` has the same security properties as running a script in Node.js (ie none). Definition: `-A, --allow-all` ```sh deno run -A script.ts deno run --allow-all script.ts ``` By default, Deno will not generate a stack trace for permission requests as it comes with a hit to performance. Users can enable stack traces with the `DENO_TRACE_PERMISSIONS` environment variable to `1`. Deno can also generate an audit log of all accessed permissions, regardless of whether the access was allowed or denied. Set `DENO_AUDIT_PERMISSIONS` to a **file path** to write JSONL — each line is an object with the following keys: - `v`: the version of the format - `datetime`: when the permission was accessed, in RFC 3339 format - `permission`: the name of the permission - `value`: the value that the permission was accessed with, or `null` if it was accessed with no value A schema for this can be found in [permission-audit.v1.json](https://github.com/denoland/deno/blob/main/cli/schemas/permission-audit.v1.json). In addition, this env var can be combined with the above-mentioned `DENO_TRACE_PERMISSIONS`, which then adds a new `stack` field to the entries which is an array containing all the stack trace frames. You can also set `DENO_AUDIT_PERMISSIONS=otel` to emit each access as an OpenTelemetry **log record** instead of writing to a file. The records are sent to whichever exporter you have configured via [`OTEL_DENO`](/runtime/fundamentals/open_telemetry/) and carry these attributes: - `deno.permission.type` - `deno.permission.value` - `deno.permission.stack` (if `DENO_TRACE_PERMISSIONS` is also set) This is the recommended setup if you already collect OpenTelemetry data — the permission audit lands next to your traces and metrics so you can correlate it with request handling. ```sh OTEL_DENO=true DENO_AUDIT_PERMISSIONS=otel deno run -A main.ts ``` ## Configuration file Deno supports storing permissions in the deno.json/deno.jsonc file. Read more under [configuration](/runtime/reference/deno_json/#permissions). ## File system access By default, executing code can not read or write arbitrary files on the file system. This includes listing the contents of directories, checking for the existence of a given file, and opening or connecting to Unix sockets. Access to read files is granted using the `--allow-read` (or `-R`) flag, and access to write files is granted using the `--allow-write` (or `-W`) flag. These flags can be specified with a list of paths to allow access to specific files or directories and any subdirectories in them. Definition: `--allow-read[=...]` or `-R[=...]` PATHs may be separated by comma (`,`) characters. To include a comma character in the PATH, it must be doubled. (Example: `this file,, contains a comma.txt`) ```sh # Allow all reads from file system deno run -R script.ts # or deno run --allow-read script.ts # Allow reads from file foo.txt and bar.txt only deno run --allow-read=foo.txt,bar.txt script.ts # Allow reads from any file in any subdirectory of ./node_modules deno run --allow-read=node_modules script.ts ``` Definition: `--deny-read[=...]` ```sh # Allow reading files in /etc but disallow reading /etc/hosts deno run --allow-read=/etc --deny-read=/etc/hosts script.ts # Deny all read access to disk, disabling permission prompts for reads. deno run --deny-read script.ts ``` Definition: `--allow-write[=...]` or `-W[=...]` ```sh # Allow all writes to file system deno run -W script.ts # or deno run --allow-write script.ts # Allow writes to file foo.txt and bar.txt only deno run --allow-write=foo.txt,bar.txt script.ts ``` Definition: `--deny-write[=...]` ```sh # Allow reading files in current working directory # but disallow writing to ./secrets directory. deno run --allow-write=./ --deny-write=./secrets script.ts # Deny all write access to disk, disabling permission prompts. deno run --deny-write script.ts ``` Some APIs in Deno are implemented using file system operations under the hood, even though they do not provide direct read/write access to specific files. These APIs read and write to disk but do not require any explicit read/write permissions. Some examples of these APIs are: - `localStorage` - Deno KV - `caches` - `Blob` Because these APIs are implemented using file system operations, users can use them to consume file system resources like storage space, even if they do not have direct access to the file system. During module loading, Deno can load files from disk. This sometimes requires explicit permissions, and sometimes is allowed by default: - All files that are imported from the entrypoint module in a way that they can be statically analyzed are allowed to be read by default. This includes static `import` statements and dynamic `import()` calls where the argument is a string literal that points to a specific file or a directory of files. The full list of files that are in this list can be printed using `deno info `. - Files that are dynamically imported in a way that can not be statically analyzed require runtime read permissions. - Files inside of a `node_modules/` directory are allowed to be read by default. When fetching modules from the network, or when transpiling code from TypeScript to JavaScript, Deno uses the file system as a cache. This means that file system resources like storage space can be consumed by Deno even if the user has not explicitly granted read/write permissions. ### Symbolic links When reading or writing through a symbolic link, Deno checks permissions based on the symlink's location, not the target it points to. This means if you have `--allow-read=/app`, you can read through a symlink at `/app/link` even if it points to a file outside `/app`. However, Deno prevents privilege escalation through symlinks. If a symlink resolves to a sensitive system path, additional permissions are required: - **`/proc`, `/dev`, `/sys` (Linux)**: Reading or writing through symlinks that resolve to these paths requires `--allow-all`, as these paths can expose sensitive system information. - **`/proc/**/environ`**: Requires `--allow-env` since it exposes environment variables. - **`/dev/null`, `/dev/zero`, `/dev/random`, `/dev/urandom`**: These safe device files are always accessible without additional permissions. Creating symlinks with [`Deno.symlink()`](/api/deno/~/Deno.symlink) requires both `--allow-read` and `--allow-write` with full access (not path-specific), because symlinks can point to arbitrary locations. > **Note**: Symlinks that already exist on the filesystem can be read through > using the permissions for the symlink's location. The full read/write > permission requirement only applies to _creating_ new symlinks with > [`Deno.symlink()`](/api/deno/~/Deno.symlink). ## Network access By default, executing code can not make network requests, open network listeners or perform DNS resolution. This includes making HTTP requests, opening TCP/UDP sockets, and listening for incoming connections on TCP or UDP. Network access is granted using the `--allow-net` flag. This flag can be specified with a list of hosts to allow access to specific network addresses. A host can be a hostname or IP address, optionally with a port. Hostnames do not allow subdomains, unless explicitly listed. To allow any subdomain for a hostname, `*` can be used as wildcard for any subdomain. Definition: `--allow-net[=...]` or `-N[=...]` ```sh # Allow network access deno run -N script.ts # or deno run --allow-net script.ts # Allow network access to github.com and jsr.io deno run --allow-net=github.com,jsr.io script.ts # Allow all subdomains for example.com deno run --allow-net="*.example.com" script.ts # A hostname at port 80: deno run --allow-net=example.com:80 script.ts # An IPv4 address on port 443 deno run --allow-net=1.1.1.1:443 script.ts # An IPv6 address, all ports allowed deno run --allow-net=[2606:4700:4700::1111] script.ts ``` Definition: `--deny-net[=...]` ```sh # Allow access to network, but deny access # to github.com and jsr.io deno run --allow-net --deny-net=github.com,jsr.io script.ts # Deny all network access, disabling permission prompts. deno run --deny-net script.ts ``` During module loading, Deno can load modules from the network. By default Deno allows loading modules from the following locations using both static and dynamic imports, without requiring explicit network access: - `https://deno.land/` - `https://jsr.io/` - `https://esm.sh/` - `https://raw.githubusercontent.com` - `https://gist.githubusercontent.com` These locations are trusted "public good" registries that are not expected to enable data exfiltration through URL paths. You can add more trusted registries using the `--allow-import` flag. In addition Deno allows importing any NPM package through `npm:` specifiers. Deno also sends requests to `https://dl.deno.land/` at most once a day to check for updates to the Deno CLI. This can be disabled using `DENO_NO_UPDATE_CHECK=1` environment var. ## Environment variables By default, executing code can not read or write environment variables. This includes reading environment variables, and setting new values. Access to environment variables is granted using the `--allow-env` flag. This flag can be specified with a list of environment variables to allow access to specific environment variables. Starting with Deno v2.1, you can now specify suffix wildcards to allow “scoped” access to environmental variables. Definition: `--allow-env[=...]` or `-E[=...]` ```sh # Allow access to all environment variables deno run -E script.ts # or deno run --allow-env script.ts # Allow HOME and FOO environment variables deno run --allow-env=HOME,FOO script.ts # Allow access to all environment variables starting with AWS_ deno run --allow-env="AWS_*" script.ts ``` Definition: `--deny-env[=...]` ```sh # Allow all environment variables except # AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY. deno run \ --allow-env \ --deny-env=AWS_ACCESS_KEY_ID,AWS_SECRET_ACCESS_KEY \ script.ts # Deny all access to env variables, disabling permission prompts. deno run --deny-env script.ts ``` The `--ignore-env` flag is similar to `--deny-env`, but instead of denying access outright, it silently returns `undefined` for any env variable reads. This is useful when you want code to run without failing on missing permissions, treating restricted variables as simply unset. Definition: `--ignore-env[=...]` ```sh # Ignore all environment variable reads (returns undefined). deno run --ignore-env script.ts # Ignore specific environment variables. deno run --ignore-env=PORT,HOME script.ts ``` > Note for Windows users: environment variables are case insensitive on Windows, > so Deno also matches them case insensitively (on Windows only). Deno reads certain environment variables on startup, such as `DENO_DIR` and `NO_COLOR` ([see the full list](/runtime/reference/cli/env_variables/)). The value of the `NO_COLOR` environment variable is visible to all code running in the Deno runtime, regardless of whether the code has been granted permission to read environment variables. ## System Information By default, executing code can not access system information, such as the operating system release, system uptime, load average, network interfaces, and system memory information. Access to system information is granted using the `--allow-sys` flag. This flag can be specified with a list of allowed interfaces from the list defined in [Deno.SysPermissionDescriptor](/api/deno/~/Deno.SysPermissionDescriptor). These strings map to functions in the `Deno` namespace that provide OS info, like [Deno.systemMemoryInfo](https://docs.deno.com/api/deno/~/Deno.SystemMemoryInfo). Definition: `--allow-sys[=...]` or `-S[=...]` ```sh # Allow all system information APIs deno run -S script.ts # or deno run --allow-sys script.ts # Allow systemMemoryInfo and osRelease APIs deno run --allow-sys="systemMemoryInfo,osRelease" script.ts ``` Definition: `--deny-sys[=...]` ```sh # Allow accessing all system information but "networkInterfaces" deno run --allow-sys --deny-sys="networkInterfaces" script.ts # Deny all access to system information, disabling permission prompts. deno run --deny-sys script.ts ``` ## Subprocesses Code executing inside of a Deno runtime can not spawn subprocesses by default, as this would constitute a violation of the principle that code can not escalate its privileges without user consent. Deno provides a mechanism for executing subprocesses, but this requires explicit permission from the user. This is done using the `--allow-run` flag. Any subprocesses you spawn from your program run independently from the permissions granted to the parent process. This means the child processes can access system resources regardless of the permissions you granted to the Deno process that spawned it. This is often referred to as privilege escalation. Because of this, make sure you carefully consider if you want to grant a program `--allow-run` access: it essentially invalidates the Deno security sandbox. If you really need to spawn a specific executable, you can reduce the risk by limiting which programs a Deno process can start by passing specific executable names to the `--allow-run` flag. Definition: `--allow-run[=...]` ```sh # Allow running all subprocesses deno run --allow-run script.ts # Allow running "curl" and "whoami" subprocesses deno run --allow-run="curl,whoami" script.ts ``` :::caution You probably don't ever want to use `--allow-run=deno` unless the parent process has `--allow-all`, as being able to spawn a `deno` process means the script can spawn another `deno` process with full permissions. ::: Definition: `--deny-run[=...]` ```sh # Allow running running all programs, but "whoami" and "ps". deno run --allow-run --deny-run="whoami,ps" script.ts # Deny all access for spawning subprocessing, disabling # permission prompts. deno run --deny-run script.ts ``` By default `npm` packages will not have their post-install scripts executed during installation (like with `deno install`), as this would allow arbitrary code execution. When running with the `--allow-scripts` flag, post-install scripts for npm packages will be executed as a subprocess. ## FFI (Foreign Function Interface) Deno provides an [FFI mechanism for executing code written in other languages](/runtime/fundamentals/ffi/), such as Rust, C, or C++, from within a Deno runtime. This is done using the [`Deno.dlopen`](/api/deno/~/Deno.dlopen) API, which can load shared libraries and call functions from them. By default, executing code can not use the [`Deno.dlopen`](/api/deno/~/Deno.dlopen) API, as this would constitute a violation of the principle that code can not escalate it's privileges without user consent. In addition to [`Deno.dlopen`](/api/deno/~/Deno.dlopen), FFI can also be used via Node-API (NAPI) native addons. These are also not allowed by default. Both [`Deno.dlopen`](/api/deno/~/Deno.dlopen) and NAPI native addons require explicit permission using the `--allow-ffi` flag. This flag can be specified with a list of files or directories to allow access to specific dynamic libraries. _Like subprocesses, dynamic libraries are not run in a sandbox and therefore do not have the same security restrictions as the Deno process they are being loaded into. Therefore, use with extreme caution._ Definition: `--allow-ffi[=...]` ```sh # Allow loading dynamic all libraries deno run --allow-ffi script.ts # Allow loading dynamic libraries from a specific path deno run --allow-ffi=./libfoo.so script.ts ``` Definition: `--deny-ffi[=...]` ```sh # Allow loading all dynamic libraries, but ./libfoo.so deno run --allow-ffi --deny-ffi=./libfoo.so script.ts # Deny loading all dynamic libraries, disabling permission prompts. deno run --deny-ffi script.ts ``` ## Importing from the Web Allow importing code from the Web. By default Deno limits hosts you can import code from. This is true for both static and dynamic imports. If you want to dynamically import code, either using the `import()` or the `new Worker()` APIs, additional permissions need to be granted. Importing from the local file system [requires `--allow-read`](#file-system-access), but Deno also allows to import from `http:` and `https:` URLs. In such case you will need to specify an explicit `--allow-import` flag: ```sh # allow importing code from `https://example.com` $ deno run --allow-import=example.com main.ts ``` By default Deno allows importing sources from following hosts: - `deno.land` - `esm.sh` - `jsr.io` - `cdn.jsdelivr.net` - `raw.githubusercontent.com` - `gist.githubusercontent.com` Imports are only allowed using HTTPS. This allow list is applied by default for static imports, and by default to dynamic imports if the `--allow-import` flag is specified. ```sh # allow dynamically importing code from `https://deno.land` $ deno run --allow-import main.ts ``` Note that specifying an allow list for `--allow-import` will override the list of default hosts.