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README.md
Chisel
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.
Authenticated connections; authenticated client connections with a users config file, authenticated server connections with fingerprint matching.
Client auto-reconnects with exponential 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)
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Clients optionally allow SOCKS5 connections from a reversed port forward
Client connections over stdio which supports ssh -o ProxyCommand providing SSH over HTTP
Install
Binaries
See the latest release 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 or earlier.
Docker
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.
sudo dnf -y install chisel
Source
$ 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 deploys this chisel server to fly.io's free allowance:
$ 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.:
$ chisel client https://<your-app>.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.
Usage
$ 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
$ 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:
{
"<user:pass>": ["<addr-regex>","<addr-regex>"]
}
when <user> connects, their <pass> 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 "<remote-host>:<remote-port>" for normal remotes,
"R:<local-interface>:<local-port>" 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 <user:pass>. It is equivalent to creating an
authfile with {"<user:pass>": [""]}. 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
$ chisel client --help
Usage: chisel client [options] <server> <remote> [remote] [remote] ...
<server> is the URL to the chisel server.
<remote>s are remote connections tunneled through the server, each of
which come in the form:
<local-host>:<local-port>:<remote-host>:<remote-port>/<protocol>
■ 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 <remote-host>:<remote-port> from the server to the client
as <local-host>:<local-port>, or:
R:<local-interface>:<local-port>:<remote-host>:<remote-port>/<protocol>
which does reverse port forwarding, sharing <remote-host>:<remote-port>
from the client to the server's <local-interface>:<local-port>.
example remotes
3000
example.com:3000
3000:google.com:80
192.168.0.5:3000:google.com:80
socks
5000:socks
udpsocks
5000:udpsocks
R:2222:localhost:22
R:socks
R:5000:socks
R:5000:udpsocks
stdio:example.com:22
1.1.1.1:53/udp
When the chisel server has --socks5 enabled, remotes can
specify "socks" or "udpsocks" in place of remote-host and
remote-port. Both default to the local host and port
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.
The "socks" remote supports TCP CONNECT only. Use "udpsocks"
for TCP CONNECT and UDP ASSOCIATE, including "R:udpsocks".
It binds TCP and UDP on the same configured interface and port;
the UDP relay never uses a randomly allocated listening port.
UDP requires support on both Chisel peers. Destination names are
resolved at the exit node. If UDP cannot bind, TCP remains available
and UDP ASSOCIATE fails; no alternate port is used. Clients using
a zero UDP source port allow one pending association per source IP
until the first valid datagram pins it. BIND, UDP fragmentation,
and udpsocks over stdio are not supported.
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: "<user>:<pass>". 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 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):
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
Print a new private key to the terminal
chisel server --keygen -
# or save it to disk --keygen /path/to/mykey
Start your chisel server
jpillora/chisel server --keyfile '<ck-base64 string or file path>' -p 9312 --socks5
Connect your chisel client (using server's fingerprint)
chisel client --fingerprint '<see server output>' <server-address>:9312 socks
Point your SOCKS5 clients (e.g. OS/Browser) to:
<client-address>:1080
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).
For setup commands, reverse mode, and a UDP client example, see the SOCKS5 UDP user guide.
Ordinary socks remotes support TCP CONNECT only and bind no UDP socket. To enable both TCP CONNECT and UDP ASSOCIATE, use udpsocks (or R:udpsocks for reverse mode), for example 1080:udpsocks. Both types default to 127.0.0.1:1080 and use the same SOCKS access permissions. A udpsocks listener binds TCP and UDP on the same configured interface and port, sharing one UDP relay socket across associations without allocating random listening ports. UDP clients keep their TCP control connection open and send SOCKS-encapsulated datagrams to that port. Datagram destination names are resolved at the exit node, and the UDP traffic travels through the encrypted SSH tunnel. Upgrade both Chisel peers for UDP; TCP SOCKS remains compatible with older peers.
When exposing a udpsocks listener through a firewall or container, allow both TCP and UDP on its configured port. UDP ASSOCIATE returns the local IP accepting the TCP connection, which must be reachable by the SOCKS client. For Linux Docker listeners, use --network host with the remote 0.0.0.0:1080:udpsocks to avoid advertising an isolated container address. Container port mappings need both -p 1080:1080/tcp and -p 1080:1080/udp, plus reachability to the advertised relay IP. If the UDP port is occupied, Chisel logs that UDP is unavailable, retains TCP service, and rejects UDP ASSOCIATE without using an alternate port; restart the proxy after freeing the port.
An association accepts packets from its TCP peer's IP. A declared UDP source port reserves that endpoint; a zero source port is pinned by its first valid datagram. Only one unpinned association per IP is allowed, so clients sharing an IP should declare their UDP source ports or send the first datagram before opening another association. Duplicate source-port reservations are rejected. Closing the control connection or losing SSH ends the association; reconnecting requires a new UDP ASSOCIATE. BIND, UDP fragmentation, and stdio:udpsocks are unsupported.
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):
chisel server --reverse --authfile users.json
chisel client --auth exituser:password <server-address> R:socks
# server-side consumers point SOCKS5 clients at 127.0.0.1:1080,
# and their traffic exits via the chisel client's network
Use R:udpsocks in the client command to also enable UDP ASSOCIATE on the same server port; the authfile grant stays the same.
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 | both | 30s | tcp target dial, SOCKS handshake, and SOCKS UDP DNS timeout |
| 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 (includes the SOCKS UDP header) |
| UDP_DEADLINE | both | 15s | udp flow read deadline and return-peer expiry; SOCKS UDP destination idle timeout |
| UDP_MAX_CONNS | both | 100 | max udp flows or return peers; SOCKS UDP associations per listener and destinations per association |
| 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.
SOCKS UDP uses hard association and destination limits and drops packets beyond them. Each association queues up to 16 outbound datagrams; full queues drop packets without blocking other clients. For SOCKS UDP, nonpositive size/connection limits or idle deadlines use the defaults, and packet size is capped at 65507 bytes. Operating systems can impose a smaller UDP send limit: macOS defaults to 9216 bytes (net.inet.udp.maxdgram). The default 9012-byte Chisel limit fits within that bound.
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 scratchDocker 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:
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. Denied requests are logged server-side as Denied connection to socks (ACL).
--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).
--auth values must be <user>:<pass> — strings without a colon now fail at startup instead of silently disabling authentication.
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.
