curl-impersonate

A special build of curl that can impersonate the four major browsers: Chrome, Edge, Safari & Firefox. curl-impersonate is able to perform TLS and HTTP handshakes that are identical to that of a real browser.

curl-impersonate can be used either as a command line tool, similar to the regular curl, or as a library that can be integrated instead of the regular libcurl. See Usage below.

Why?

When you use an HTTP client with a TLS website, it first performs a TLS handshake. The first message of that handshake is called Client Hello. The Client Hello message that most HTTP clients and libraries produce differs drastically from that of a real browser.

If the server uses HTTP/2, then in addition to the TLS handshake there is also an HTTP/2 handshake where various settings are exchanged. The settings that most HTTP clients and libraries use differ as well from those of any real browsers.

For these reasons, some web services use the TLS and HTTP handshakes to fingerprint which client is accessing them, and then present different content for different clients. These methods are known as TLS fingerprinting and HTTP/2 fingerprinting respectively. Their widespread use has led to the web becoming less open, less private and much more restrictive towards specific web clients

With the modified curl in this repository, the TLS and HTTP handshakes look exactly like those of a real browser.

How?

To make this work, curl was patched significantly to resemble a browser. Specifically, The modifications that were needed to make this work:

• Compiling curl with nss, the TLS library that Firefox uses, instead of OpenSSL. For the Chrome version, compiling with BoringSSL, Google's TLS library.
• Modifying the way curl configures various TLS extensions and SSL options.
• Adding support for new TLS extensions.
• Changing the settings that curl uses for its HTTP/2 connections.
• Running curl with some non-default flags, for example --ciphers, --curves and some -H headers.

The resulting curl looks, from a network perspective, identical to a real browser.

Read the full technical description in the blog posts: part a, part b.

Supported browsers

The following browsers can be impersonated.

Browser	Version	Build	OS	Target name	Wrapper script
	99	99.0.4844.51	Windows 10	chrome99	curl_chrome99
	100	100.0.4896.75	Windows 10	chrome100	curl_chrome100
	101	101.0.4951.67	Windows 10	chrome101	curl_chrome101
	104	104.0.5112.81	Windows 10	chrome104	curl_chrome104
	107	107.0.5304.107	Windows 10	chrome107	curl_chrome107
	110	110.0.5481.177	Windows 10	chrome110	curl_chrome110
	116	116.0.5845.180	Windows 10	chrome116	curl_chrome116
	99	99.0.4844.73	Android 12	chrome99_android	curl_chrome99_android
	99	99.0.1150.30	Windows 10	edge99	curl_edge99
	101	101.0.1210.47	Windows 10	edge101	curl_edge101
	91 ESR	91.6.0esr	Windows 10	ff91esr	curl_ff91esr
	95	95.0.2	Windows 10	ff95	curl_ff95
	98	98.0	Windows 10	ff98	curl_ff98
	100	100.0	Windows 10	ff100	curl_ff100
	102	102.0	Windows 10	ff102	curl_ff102
	109	109.0	Windows 10	ff109	curl_ff109
	117	117.0.1	Windows 10	ff117	curl_ff117
	15.3	16612.4.9.1.8	MacOS Big Sur	safari15_3	curl_safari15_3
	15.5	17613.2.7.1.8	MacOS Monterey	safari15_5	curl_safari15_5

This list is also available in the browsers.json file.

Basic usage

For each supported browser there is a wrapper script that launches curl-impersonate with all the needed headers and flags. For example:

curl_chrome116 https://www.wikipedia.org

You can add command line flags and they will be passed on to curl. However, some flags change curl's TLS signature which may cause it to be detected.

Please note that the wrapper scripts use a default set of HTTP headers. If you want to change these headers, you may want to modify the wrapper scripts to fit your own purpose.

See Advanced usage for more options, including using libcurl-impersonate as a library.

Documentation

More documentation is available in the docs/ directory.

Installation

There are two versions of curl-impersonate for technical reasons. The chrome version is used to impersonate Chrome, Edge and Safari. The firefox version is used to impersonate Firefox.

Pre-compiled binaries

Pre-compiled binaries for Linux and macOS (Intel) are available at the GitHub releases page. Before you use them you need to install nss (Firefox's TLS library) and CA certificates:

• Ubuntu - sudo apt install libnss3 nss-plugin-pem ca-certificates
• Red Hat/Fedora/CentOS - yum install nss nss-pem ca-certificates
• Archlinux - pacman -S nss ca-certificates
• macOS - brew install nss ca-certificates

The pre-compiled binaries contain libcurl-impersonate and a statically compiled curl-impersonate for ease of use.

The pre-compiled Linux binaries are built for Ubuntu systems. On other distributions if you have errors with certificate verification you may have to tell curl where to find the CA certificates. For example:

curl_chrome116 https://www.wikipedia.org --cacert /etc/ssl/certs/ca-bundle.crt

Also make sure to read Notes on Dependencies.

Building from source

See INSTALL.md.

Docker images

Docker images based on Alpine Linux and Debian with curl-impersonate compiled and ready to use are available on Docker Hub. The images contain the binary and all the wrapper scripts. Use like the following:

# Firefox version, Alpine Linux
docker pull lwthiker/curl-impersonate:0.5-ff
docker run --rm lwthiker/curl-impersonate:0.5-ff curl_ff109 https://www.wikipedia.org

# Chrome version, Alpine Linux
docker pull lwthiker/curl-impersonate:0.5-chrome
docker run --rm lwthiker/curl-impersonate:0.5-chrome curl_chrome110 https://www.wikipedia.org

Distro packages

AUR packages are available to Archlinux users:

• Pre-compiled package: curl-impersonate-bin, libcurl-impersonate-bin.
• Build from source code: curl-impersonate-chrome, curl-impersonate-firefox.

Advanced usage

libcurl-impersonate

libcurl-impersonate.so is libcurl compiled with the same changes as the command line curl-impersonate. It has an additional API function:

CURLcode curl_easy_impersonate(struct Curl_easy *data, const char *target,
                               int default_headers);

You can call it with the target names, e.g. chrome116, and it will internally set all the options and headers that are otherwise set by the wrapper scripts. If default_headers is set to 0, the built-in list of HTTP headers will not be set, and the user is expected to provide them instead using the regular CURLOPT_HTTPHEADER libcurl option.

Calling the above function sets the following libcurl options:

• CURLOPT_HTTP_VERSION
• CURLOPT_SSLVERSION, CURLOPT_SSL_CIPHER_LIST, CURLOPT_SSL_EC_CURVES, CURLOPT_SSL_ENABLE_NPN, CURLOPT_SSL_ENABLE_ALPN
• CURLOPT_HTTPBASEHEADER, if default_headers is non-zero (this is a non-standard HTTP option created for this project).
• CURLOPT_HTTP2_PSEUDO_HEADERS_ORDER, CURLOPT_HTTP2_NO_SERVER_PUSH (non-standard HTTP/2 options created for this project).
• CURLOPT_SSL_ENABLE_ALPS, CURLOPT_SSL_SIG_HASH_ALGS, CURLOPT_SSL_CERT_COMPRESSION, CURLOPT_SSL_ENABLE_TICKET (non-standard TLS options created for this project).
• CURLOPT_SSL_PERMUTE_EXTENSIONS (non-standard TLS options created for this project). Note that if you call curl_easy_setopt() later with one of the above it will override the options set by curl_easy_impersonate().

Using CURL_IMPERSONATE env var

If your application uses libcurl already, you can replace the existing library at runtime with LD_PRELOAD (Linux only). You can then set the CURL_IMPERSONATE env var. For example:

LD_PRELOAD=/path/to/libcurl-impersonate.so CURL_IMPERSONATE=chrome116 my_app

The CURL_IMPERSONATE env var has two effects:

• curl_easy_impersonate() is called automatically for any new curl handle created by curl_easy_init().
• curl_easy_impersonate() is called automatically after any curl_easy_reset() call.

This means that all the options needed for impersonation will be automatically set for any curl handle.

If you need precise control over the HTTP headers, set CURL_IMPERSONATE_HEADERS=no to disable the built-in list of HTTP headers, then set them yourself with curl_easy_setopt(). For example:

LD_PRELOAD=/path/to/libcurl-impersonate.so CURL_IMPERSONATE=chrome116 CURL_IMPERSONATE_HEADERS=no my_app

Note that the LD_PRELOAD method will NOT WORK for curl itself because the curl tool overrides the TLS settings. Use the wrapper scripts instead.

Notes on dependencies

If you intend to copy the self-compiled artifacts to another system, or use the Pre-compiled binaries provided by the project, make sure that all the additional dependencies are met on the target system as well. In particular, see the note about the Firefox version.

Contents

This repository contains two main folders:

• chrome - Scripts and patches for building the Chrome version of curl-impersonate.
• firefox - Scripts and patches for building the Firefox version of curl-impersonate.

The layout is similar for both. For example, the Firefox directory contains:

• Dockerfile - Used to build curl-impersonate with all dependencies.
• curl_ff91esr, curl_ff95, curl_ff98 - Wrapper scripts that launch curl-impersonate with the correct flags.
• curl-impersonate.patch - The main patch that makes curl use the same TLS extensions as Firefox. Also makes curl compile statically with libnghttp2 and libnss.

Other files of interest:

• tests/signatures - YAML database of known browser signatures that can be impersonated.

Contributing

If you'd like to help, please check out the open issues. You can open a pull request with your changes.

This repository contains the build process for curl-impersonate. The actual patches to curl are maintained in a separate repository forked from the upstream curl. The changes are maintained in the impersonate-firefox and impersonate-chrome branches.

Sponsors

Sponsors help keep this project open and maintained. If you wish to become a sponsor, please contact me directly at: lwt at lwthiker dot com.