# Chisel [![GoDoc](https://godoc.org/github.com/jpillora/chisel?status.svg)](https://godoc.org/github.com/jpillora/chisel) [![CI](https://github.com/jpillora/chisel/workflows/CI/badge.svg)](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. ![overview](https://docs.google.com/drawings/d/1p53VWxzGNfy8rjr-mW8pvisJmhkoLl82vAgctO_6f1w/pub?w=960&h=720) ## 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 [![Releases](https://img.shields.io/github/release/jpillora/chisel.svg)](https://github.com/jpillora/chisel/releases) [![Releases](https://img.shields.io/github/downloads/jpillora/chisel/total.svg)](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 [![Docker Pulls](https://img.shields.io/docker/pulls/jpillora/chisel.svg)](https://hub.docker.com/r/jpillora/chisel/) [![Image Size](https://img.shields.io/docker/image-size/jpillora/chisel/latest)](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 ``` ``` plain $ chisel server --help Usage: chisel server [options] Options: --host, Defines the HTTP listening host – the network interface (defaults the environment variable HOST and falls back to 0.0.0.0). --port, -p, Defines the HTTP listening port (defaults to the environment variable PORT and falls back to port 8080). --key, (deprecated use --keygen and --keyfile instead) An optional string to seed the generation of a ECDSA public and private key pair. All communications will be secured using this key pair. Share the subsequent fingerprint with clients to enable detection of man-in-the-middle attacks (defaults to the CHISEL_KEY environment variable, otherwise a new key is generate each run). --keygen, A path to write a newly generated PEM-encoded SSH private key file. If users depend on your --key fingerprint, you may also include your --key to output your existing key. Use - (dash) to output the generated key to stdout. --keyfile, An optional path to a PEM-encoded SSH private key. When this flag is set, the --key option is ignored, and the provided private key is used to secure all communications. (defaults to the CHISEL_KEY_FILE environment variable). Since ECDSA keys are short, you may also set keyfile to the inline key string itself, exactly as printed by --keygen (a base64 string with a "ck-" prefix); no extra base64 encoding is needed. --authfile, An optional path to a users.json file. This file should be an object with users defined like: { "": ["",""] } when connects, their will be verified and then each of the remote addresses will be compared against the list of address regular expressions for a match. Patterns are NOT anchored by default: "10.0.0.1:80" also matches "210.0.0.1:8080", and "." matches any character. Anchor your patterns, e.g. "^10\.0\.0\.1:80$". The empty string "" matches every address. Addresses will always come in the form ":" for normal remotes, "R::" for reverse port forwarding remotes, and "socks" for SOCKS5 proxy access. Note that SOCKS5 access previously bypassed this list; existing authfiles which should allow SOCKS5 must add an entry matching "socks" (the empty wildcard "" matches everything, including "socks"). This file will be automatically reloaded on change. Reloads apply to new connections and to new tunnels of connected clients; established tunnels are not interrupted. --auth, An optional string representing a single user with full access, in the form of . It is equivalent to creating an authfile with {"": [""]}. If unset, it will use the environment variable AUTH. --keepalive, An optional keepalive interval. Since the underlying transport is HTTP, in many instances we'll be traversing through proxies, often these proxies will close idle connections. You must specify a time with a unit, for example '5s' or '2m'. Defaults to '25s' (set to 0s to disable). --backend, Specifies another HTTP server to proxy requests to when chisel receives a normal HTTP request. Useful for hiding chisel in plain sight. --proxy is accepted as an alias for this flag. --socks5, Allow clients to access the internal SOCKS5 proxy. See chisel client --help for more information. --reverse, Allow clients to specify reverse port forwarding remotes in addition to normal remotes. --tls-key, Enables TLS and provides optional path to a PEM-encoded TLS private key. When this flag is set, you must also set --tls-cert, and you cannot set --tls-domain. --tls-cert, Enables TLS and provides optional path to a PEM-encoded TLS certificate. When this flag is set, you must also set --tls-key, and you cannot set --tls-domain. --tls-domain, Enables TLS and automatically acquires a TLS key and certificate using LetsEncrypt. Setting --tls-domain requires port 443. You may specify multiple --tls-domain flags to serve multiple domains. The resulting files are cached in the "$HOME/.cache/chisel" directory. You can modify this path by setting the CHISEL_LE_CACHE variable, or disable caching by setting this variable to "-". You can optionally provide a certificate notification email by setting CHISEL_LE_EMAIL. --tls-ca, a path to a PEM encoded CA certificate bundle or a directory holding multiple PEM encode CA certificate bundle files, which is used to validate client connections. The provided CA certificates will be used instead of the system roots. This is commonly used to implement mutual-TLS. --pid Generate pid file in current working directory -v, Enable verbose logging --help, This help text Signals: The chisel process is listening for: a SIGINT or SIGTERM to begin a graceful shutdown (a second signal forces an immediate exit), a SIGUSR2 to print process stats, and a SIGHUP to short-circuit the client reconnect timer Version: X.Y.Z Read more: https://github.com/jpillora/chisel ``` ``` plain $ chisel client --help Usage: chisel client [options] [remote] [remote] ... is the URL to the chisel server. s are remote connections tunneled through the server, each of which come in the form: :::/ ■ local-host defaults to 0.0.0.0 (all interfaces). ■ local-port defaults to remote-port. ■ remote-port is required*. ■ remote-host defaults to 127.0.0.1 (server localhost). ■ protocol defaults to tcp. which shares : from the server to the client as :, or: R::::/ which does reverse port forwarding, sharing : from the client to the server's :. example remotes 3000 example.com:3000 3000:google.com:80 192.168.0.5:3000:google.com:80 socks 5000:socks R:2222:localhost:22 R:socks R:5000:socks stdio:example.com:22 1.1.1.1:53/udp When the chisel server has --socks5 enabled, remotes can specify "socks" in place of remote-host and remote-port. The default local host and port for a "socks" remote is 127.0.0.1:1080. Connections to this remote will terminate at the server's internal SOCKS5 proxy. When the server also has --authfile set, SOCKS5 access requires an entry matching the token "socks" in the user's address list. When the chisel server has --reverse enabled, remotes can be prefixed with R to denote that they are reversed. That is, the server will listen and accept connections, and they will be proxied through the client which specified the remote. Reverse remotes specifying "R:socks" will listen on the server's default socks port (1080) and terminate the connection at the client's internal SOCKS5 proxy. When stdio is used as local-host, the tunnel will connect standard input/output of this program with the remote. This is useful when combined with ssh ProxyCommand. You can use ssh -o ProxyCommand='chisel client chiselserver stdio:%h:%p' \ user@example.com to connect to an SSH server through the tunnel. Options: --fingerprint, A *strongly recommended* fingerprint string to perform host-key validation against the server's public key. Fingerprint mismatches will close the connection. Fingerprints are generated by hashing the ECDSA public key using SHA256 and encoding the result in base64. Fingerprints must be 44 characters containing a trailing equals (=). Legacy MD5 colon fingerprints (deprecated) are still accepted, but only in their full 16-octet form; truncated prefixes are rejected. --auth, An optional username and password (client authentication) in the form: ":". These credentials are compared to the credentials inside the server's --authfile. defaults to the AUTH environment variable. --keepalive, An optional keepalive interval. Since the underlying transport is HTTP, in many instances we'll be traversing through proxies, often these proxies will close idle connections. You must specify a time with a unit, for example '5s' or '2m'. Defaults to '25s' (set to 0s to disable). --max-retry-count, Maximum number of times to retry before exiting. Defaults to unlimited. --min-retry-interval, Minimum wait time before retrying after a disconnection. Defaults to 1 second. --max-retry-interval, Maximum wait time before retrying after a disconnection. Defaults to 5 minutes. --proxy, An optional HTTP CONNECT or SOCKS5 proxy which will be used to reach the chisel server. Authentication can be specified inside the URL. Credentials must be URL-encoded; for example a "#" in the password must be written as "%23". For example, http://admin:password@my-server.com:8081 or: socks://admin:password@my-server.com:1080 The socks://, socks5:// and socks5h:// schemes are equivalent: DNS is always resolved by the proxy. --header, Set a custom header in the form "HeaderName: HeaderContent". Can be used multiple times. (e.g --header "Foo: Bar" --header "Hello: World") --hostname, Optionally set the 'Host' header (defaults to the host found in the server url). --sni, Override the ServerName when using TLS (defaults to the hostname). --tls-ca, An optional root certificate bundle used to verify the chisel server. Only valid when connecting to the server with "https" or "wss". By default, the operating system CAs will be used. --tls-skip-verify, Skip server TLS certificate verification of chain and host name (if TLS is used for transport connections to server). If set, client accepts any TLS certificate presented by the server and any host name in that certificate. This only affects transport https (wss) connection. Chisel server's public key may be still verified (see --fingerprint) after inner connection is established. --tls-key, a path to a PEM encoded private key used for client authentication (mutual-TLS). --tls-cert, a path to a PEM encoded certificate matching the provided private key. The certificate must have client authentication enabled (mutual-TLS). --pid Generate pid file in current working directory -v, Enable verbose logging --help, This help text Signals: The chisel process is listening for: a SIGINT or SIGTERM to begin a graceful shutdown (a second signal forces an immediate exit), a SIGUSR2 to print process stats, and a SIGHUP to short-circuit the client reconnect timer Version: X.Y.Z Read more: https://github.com/jpillora/chisel ``` ### 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` | both | `15s` | udp flow read deadline and return-peer expiry | | `UDP_MAX_CONNS` | both | `100` | max udp flows or return peers 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` - 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 - release binaries are built with Go 1.27.0; `x/crypto/ssh` is updated to v0.55.0 to address GO-2026-6303 - releases now ship ko-built, scratch-based multi-arch images with CA roots to GHCR and Docker Hub; 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