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August 27, 2020 09:41
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Cloudflare http handler in C# allows scraping cloudflare protected websites
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using System; | |
using System.Net.Http; | |
using System.Threading.Tasks; | |
using System.Text.RegularExpressions; | |
using System.Threading; | |
using System.Collections.Generic; | |
using System.Linq; | |
using Microsoft.ClearScript.V8; | |
using HtmlAgilityPack; | |
/// <summary> | |
/// A custom Http handler for Cloudflare protected servers | |
/// </summary> | |
public class CloudflareHttpHandler : HttpClientHandler | |
{ | |
protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) | |
{ | |
var task = base.SendAsync(request, cancellationToken); | |
var response = task.Result; | |
if(base.CookieContainer.GetCookieHeader(request.RequestUri).Contains("cf_clearance")) | |
return task; | |
IEnumerable<string> values; | |
if(response.Headers.TryGetValues("refresh", out values) && values.FirstOrDefault().Contains("URL=/cdn-cgi/") && response.Headers.Server.ToString() == "cloudflare-nginx" ) | |
{ | |
Console.WriteLine("Solving cloudflare challenge . . . "); | |
string content = response.Content.ReadAsStringAsync().Result; | |
var htmlDocument = new HtmlDocument(); | |
htmlDocument.LoadHtml(content); | |
var jschl_vc = htmlDocument.DocumentNode.SelectSingleNode(@".//input[@name=""jschl_vc""]").Attributes["value"].Value; | |
var pass = htmlDocument.DocumentNode.SelectSingleNode(@".//input[@name=""pass""]").Attributes["value"].Value; | |
var script = htmlDocument.DocumentNode.SelectSingleNode(@".//script").InnerText; | |
var regex = new string[3] { | |
@"setTimeout\(function\(\){(.+)},\s*\d*\s*\)\s*;", | |
@"^\n*\s*(var\s+.*?;)", | |
@"(?<=\s+;)(.+t.length;)" | |
}; | |
string function, vars, calc; | |
function = Regex.Match(script, regex[0], RegexOptions.Singleline).Value; | |
vars = Regex.Match(function, regex[1], RegexOptions.Multiline).Value; | |
calc = Regex.Match(function, regex[2], RegexOptions.Singleline).Value | |
.Replace("a.value", "var result") | |
.Replace("t.length", (request.RequestUri.Host.Length).ToString());; | |
object result; | |
using(var engine = new V8ScriptEngine()) | |
result = engine.Evaluate("function getAnswer() {" + vars + calc + "return result;" + "} getAnswer();"); | |
Thread.Sleep(5000); | |
var requestUri = request.RequestUri; | |
request.RequestUri = new Uri(requestUri, String.Format("cdn-cgi/l/chk_jschl?jschl_vc={0}&pass={1}&jschl_answer={2}", jschl_vc, pass, result.ToString())); | |
base.SendAsync(request, cancellationToken).Wait(); | |
request.RequestUri = requestUri; | |
return base.SendAsync(request, cancellationToken); | |
} | |
return task; | |
} | |
} |
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