# Chisel [](https://godoc.org/github.com/jpillora/chisel) [](https://github.com/jpillora/chisel/actions?workflow=CI) Chisel is a fast TCP/UDP tunnel, transported over HTTP, secured via SSH. Single executable including both client and server. Written in Go (golang). Chisel is mainly useful for passing through firewalls, though it can also be used to provide a secure endpoint into your network. ## Table of Contents - [Features](#features) - [Install](#install) - [Demo](#demo) - [Usage](#usage) - [Contributing](#contributing) - [Changelog](#changelog) - [License](#license) ## Features - Easy to use - [Performant](./test/bench/perf.md)\* - [Encrypted connections](#security) using the SSH protocol (via `crypto/ssh`) - [Authenticated connections](#authentication); authenticated client connections with a users config file, authenticated server connections with fingerprint matching. - Client auto-reconnects with [exponential backoff](https://github.com/jpillora/backoff) (tunable via `--min/max-retry-interval`); keepalive pings time out, so silently dead connections (sleep/wake, NAT timeouts, server restarts) are detected and re-established - Clients can create multiple tunnel endpoints over one TCP connection - Clients can optionally pass through SOCKS or HTTP CONNECT proxies - Reverse port forwarding (Connections go through the server and out the client) - Server optionally doubles as a [reverse proxy](http://golang.org/pkg/net/http/httputil/#NewSingleHostReverseProxy) - Server optionally allows [SOCKS5](https://en.wikipedia.org/wiki/SOCKS) connections (See [guide below](#socks5-guide)) - Clients optionally allow [SOCKS5](https://en.wikipedia.org/wiki/SOCKS) connections from a reversed port forward - Client connections over stdio which supports `ssh -o ProxyCommand` providing SSH over HTTP ## Install ### Binaries [](https://github.com/jpillora/chisel/releases) [](https://github.com/jpillora/chisel/releases) See [the latest release](https://github.com/jpillora/chisel/releases/latest) or download and install it now with `curl https://i.jpillora.com/chisel! | bash` Binaries are built with the latest Go release, which sets the minimum OS versions: Windows 10 / Server 2016, macOS 12, Linux kernel 3.2, FreeBSD 12.2. For older systems (e.g. Windows 7), use [release v1.8.1](https://github.com/jpillora/chisel/releases/tag/v1.8.1) or earlier. ### Docker [](https://hub.docker.com/r/jpillora/chisel/) [](https://hub.docker.com/r/jpillora/chisel/tags) ```sh docker run --rm -it jpillora/chisel --help ``` Images are multi-arch and published to both Docker Hub (`jpillora/chisel`) and GitHub Container Registry (`ghcr.io/jpillora/chisel`). ### Fedora The package is maintained by the Fedora community. If you encounter issues related to the usage of the RPM, please use this [issue tracker](https://bugzilla.redhat.com/buglist.cgi?bug_status=NEW&bug_status=ASSIGNED&classification=Fedora&component=chisel&list_id=11614537&product=Fedora&product=Fedora%20EPEL). ```sh sudo dnf -y install chisel ``` ### Source ```sh $ go install github.com/jpillora/chisel@latest ``` ## Demo You can run your own demo server in minutes (the old Heroku demo went away with Heroku's free tier). [`example/fly.toml`](example/fly.toml) deploys this `chisel server` to [fly.io](https://fly.io)'s free allowance: ```sh $ chisel server --port $PORT --backend http://example.com # listens on $PORT, proxies normal web requests to http://example.com ``` Deploy it with `fly launch --copy-config` from the `example/` directory, then tunnel to any service running beside the server, e.g.: ```sh $ chisel client https://.fly.dev 3000 # connects to your chisel server, # tunnels your localhost:3000 to the server's localhost:3000 ``` Visiting your app's URL in a browser hits the server's default backend proxy and shows a copy of [example.com](http://example.com). ## Usage ``` plain $ chisel --help Usage: chisel [command] [--help] Version: X.Y.Z Commands: server - runs chisel in server mode client - runs chisel in client mode Read more: https://github.com/jpillora/chisel ``` ``` /* Detailed source-code truncated for AI context efficiency. */ ``` ``` /* Detailed source-code truncated for AI context efficiency. */ ``` ### Security Encryption is always enabled. When you start up a chisel server, it will generate an in-memory ECDSA public/private key pair. The public key fingerprint (base64 encoded SHA256) will be displayed as the server starts. Instead of generating a random key, the server may optionally specify a key file, using the `--keyfile` option. When clients connect, they will also display the server's public key fingerprint. The client can force a particular fingerprint using the `--fingerprint` option. Legacy MD5 fingerprints are still accepted but must be the full 16-octet colon form — truncated prefixes are rejected. See the `--help` above for more information. The server also caps inbound websocket message sizes before authentication (`CHISEL_WS_READ_LIMIT`, default 512 KiB), so unauthenticated peers cannot exhaust memory with oversized messages. The default sits comfortably above `x/crypto/ssh`'s 256 KiB maximum transport packet, so no valid SSH packet is ever rejected. Only `0` disables the limit; negative values fall back to the safe default. ### Authentication Using the `--authfile` option, the server may optionally provide a `user.json` configuration file to create a list of accepted users. The client then authenticates using the `--auth` option. See [users.json](example/users.json) for an example authentication configuration file. See the `--help` above for more information. Notes on authfile behavior: - The file is watched and **reloaded live** — including editor saves via rename (vim) and kubernetes configmap updates. Reloads apply to new connections and to new tunnels of already-connected clients; removed users lose access to new tunnels immediately, though established tunnels are not interrupted. - Address patterns are regular expressions and are **not anchored** — anchor them with `^` and `$` (the server warns about unanchored patterns at load). The empty string `""` matches everything. - SOCKS5 access is controlled by an entry matching the token `socks`. **Breaking**: SOCKS5 previously bypassed the authfile entirely; servers running `--socks5` with `--authfile` must grant `socks` to users who should keep proxy access (wildcard `""` entries keep working). - Auth strings without a colon (`user:pass`) are now a **fatal startup error** on both server and client — previously they silently disabled authentication. - The `--auth` user survives authfile reloads and wins name clashes with file users. Internally, this is done using the _Password_ authentication method provided by SSH. Learn more about `crypto/ssh` here http://blog.gopheracademy.com/go-and-ssh/. Session opens/closes (with user, source address and remotes) and failed login attempts are logged at info level. ### TLS Guide The simplest secure setup is `--tls-domain`, which provisions a LetsEncrypt certificate automatically (requires port 443 and a DNS record pointing at the server): ```sh chisel server --port 443 --tls-domain chisel.example.com --auth user:pass chisel client --auth user:pass https://chisel.example.com R:2222:localhost:22 ``` To use your own certificate (self-signed or internal CA), generate a key/cert pair and point both sides at the right files: ```sh chisel server --port 443 --tls-key key.pem --tls-cert cert.pem chisel client --tls-ca ca.pem https://chisel.example.com 3000 ``` For mutual TLS, also pass `--tls-ca` to the server and `--tls-cert`/`--tls-key` to each client. Note that TLS wraps chisel's transport from the outside; the inner SSH layer still encrypts and authenticates, so `--fingerprint` validation works with or without TLS. ### SOCKS5 Guide with Docker 1. Print a new private key to the terminal ```sh chisel server --keygen - # or save it to disk --keygen /path/to/mykey ``` 1. Start your chisel server ```sh jpillora/chisel server --keyfile '' -p 9312 --socks5 ``` 1. Connect your chisel client (using server's fingerprint) ```sh chisel client --fingerprint '' :9312 socks ``` 1. Point your SOCKS5 clients (e.g. OS/Browser) to: ``` :1080 ``` 1. Now you have an encrypted, authenticated SOCKS5 connection over HTTP Note: if the server also uses `--authfile`, users need an entry matching the token `socks` to use the proxy (see [Authentication](#authentication)). ### Reverse SOCKS with an Authfile To let a specific client act as a SOCKS exit node, grant it the reverse-socks listener address (`R:socks` listens on the server's `127.0.0.1:1080`): ```json { "exituser:password": ["^R:127\\.0\\.0\\.1:1080$"] } ``` ```sh chisel server --reverse --authfile users.json chisel client --auth exituser:password R:socks # server-side consumers point SOCKS5 clients at 127.0.0.1:1080, # and their traffic exits via the chisel client's network ``` See also the step-by-step [reverse tunneling example](example/reverse-tunneling-authenticated.md). ### Running behind a CDN (Cloudflare) chisel works through CDNs that support WebSockets. For Cloudflare: enable WebSockets, proxy (orange-cloud) the DNS record, and connect clients with `https://`. The CDN terminates TLS, but the inner SSH layer means `--fingerprint` validation still authenticates your chisel server end-to-end — the CDN cannot read or modify tunneled traffic. Keep `--keepalive` at its `25s` default to stay under CDN idle timeouts, and note that proxies which strip `Upgrade` headers cannot carry chisel at all. ### Tuning with environment variables Less common knobs are environment variables, all read with a `CHISEL_` prefix (e.g. `CHISEL_WS_TIMEOUT=10s`): | Variable | Side | Default | Purpose | | --------------- | ----------- | ------------------ | -------------------------------------------------- | | `WS_TIMEOUT` | client | `45s` | websocket handshake timeout | | `SSH_TIMEOUT` | client | `30s` | ssh handshake timeout | | `CONFIG_TIMEOUT`| server | `10s` | wait for the client's config request | | `SSH_WAIT` | both | `35s` | how long new tunnels wait for an active connection | | `PING_TIMEOUT` | both | keepalive interval | keepalive ping reply timeout (no pings if `--keepalive 0`) | | `DIAL_TIMEOUT` | exit node | `30s` | tcp dial timeout for tunnel targets | | `WS_READ_LIMIT` | both | `524288` | max inbound websocket message bytes (0 = no limit; negative = default) | | `WS_BUFF_SIZE` | both | go default | websocket read/write buffer sizes | | `UDP_MAX_SIZE` | both | `9012` | max udp packet bytes | | `UDP_DEADLINE` | exit node | `15s` | udp flow read deadline and idle-sweep age | | `UDP_MAX_CONNS` | exit node | `100` | max concurrent udp flows per tunnel | | `SHUTDOWN_GRACE`| server | `5s` | http request drain time on shutdown | `HOST`, `PORT`, `AUTH`, and `CHISEL_KEY`/`CHISEL_KEY_FILE` are documented in the `--help` texts above. #### Caveats Since WebSockets support is required: - IaaS providers all will support WebSockets (unless an unsupporting HTTP proxy has been forced in front of you, in which case I'd argue that you've been downgraded to PaaS) - PaaS providers vary in their support for WebSockets - Heroku has full support - Openshift has full support though connections are only accepted on ports 8443 and 8080 - Google App Engine standard has **no** support (the flexible environment does) ## Contributing - http://golang.org/doc/code.html - http://golang.org/doc/effective_go.html - `github.com/jpillora/chisel/share` contains the shared package - `github.com/jpillora/chisel/server` contains the server package - `github.com/jpillora/chisel/client` contains the client package ## Changelog - `1.0` - Initial release - `1.1` - Replaced simple symmetric encryption for ECDSA SSH - `1.2` - Added SOCKS5 (server) and HTTP CONNECT (client) support - `1.3` - Added reverse tunnelling support - `1.4` - Added arbitrary HTTP header support - `1.5` - Added reverse SOCKS support (by @aus) - `1.6` - Added client stdio support (by @BoleynSu) - `1.7` - Added UDP support - `1.8` - Move to a `scratch`Docker image - `1.9` - Bump to Go 1.21. Switch from `--key` seed to P256 key strings with `--key{gen,file}` (by @cmenginnz) - `1.10` - Bump to Go 1.22. Add `.rpm` `.deb` and `.apk` to releases. Fix bad version comparison. - `1.11` - Bump to Go 1.25.1. Update all dependencies. - `1.12` - (unreleased) Reliability and security pass: - keepalive pings now time out (`CHISEL_PING_TIMEOUT`), so dead connections reconnect promptly after sleep/wake, NAT timeouts and server restarts - authfile reloads survive editor renames and kubernetes configmap swaps, and apply live to connected clients (new tunnels; established tunnels are not interrupted) - **breaking**: with `--socks5` + `--authfile`, SOCKS5 access now requires an authfile entry matching `socks` (wildcard `""` entries keep working) - **breaking**: truncated legacy MD5 fingerprints are rejected — `--fingerprint` must be the full SHA256 form (or the full 16-octet MD5 colon form) - **breaking**: auth strings without a colon (e.g. `--auth user`) are a fatal startup error instead of silently disabling authentication - TCP half-close is propagated through tunnels, and unreachable targets reject the tunnel instead of presenting a dead connection (`CHISEL_DIAL_TIMEOUT`, default 30s) - graceful shutdown on SIGTERM with HTTP request draining (`CHISEL_SHUTDOWN_GRACE`); a second signal force-exits - UDP exit nodes no longer break or leak past 100 concurrent flows (`CHISEL_UDP_MAX_CONNS`) - inbound websocket messages are size-capped pre-auth (`CHISEL_WS_READ_LIMIT`) - server no longer panics when a client disconnects between the SSH handshake and its config request (#608) - client exits non-zero when `--max-retry-count` is exhausted; new `--min-retry-interval` (default 1s); `socks5://` accepted for `--proxy` - `go install` builds report their real version; sessions and failed logins are logged at info level - releases now ship goreleaser-built multi-arch Docker images to GHCR and Docker Hub with correctly stamped versions; releasing is two-stage — tagging builds a draft GitHub release plus version-tagged images, and publishing the draft promotes the Docker `latest` / `X` / `X.Y` tags ### Upgrading to 1.12 Four changes may require action when upgrading from 1.11.x or earlier: 1. **SOCKS5 + `--authfile`** (enforced since v1.11.7): users who should keep proxy access need an authfile entry matching the token `socks` (the wildcard `""` keeps working). See [Authentication](#authentication). Denied requests are logged server-side as `Denied connection to socks (ACL)`. 2. **`--fingerprint`**: truncated legacy MD5 fingerprints are rejected. Use the full SHA256 fingerprint printed by the server and client (the full 16-octet MD5 colon form is still accepted, but deprecated). 3. **`--auth`** values must be `:` — strings without a colon now fail at startup instead of silently disabling authentication. 4. **Exit codes**: `chisel client` with `--max-retry-count` now exits non-zero when connection attempts are exhausted; scripts checking `$?` and systemd `Restart=on-failure` units will notice. ## License [MIT](https://github.com/jpillora/chisel/blob/master/LICENSE) © Jaime Pillora