内容简介:企业通常会使用Gitlab作为内部代码管理平台,一来私有仓库更加安全,二来gitlab的功能十分完整。但仍不能保证私有仓库中的代码不被泄露到外部,于是对gitlab的权限审计以及下载审计就变得尤为重要。本文将基于gitlab-ee-11.10版本,详细叙述如何对gitlab的权限及代码下载进行审计。笔者使用了docker进行快速部署:
*本文原创作者:胡说,本文属于FreeBuf原创奖励计划,未经许可禁止转载
企业通常会使用Gitlab作为内部代码管理平台,一来私有仓库更加安全,二来gitlab的功能十分完整。但仍不能保证私有仓库中的代码不被泄露到外部,于是对gitlab的权限审计以及下载审计就变得尤为重要。本文将基于gitlab-ee-11.10版本,详细叙述如何对gitlab的权限及代码下载进行审计。
0×00 快速部署gitlab
笔者使用了 docker 进行快速部署:
docker pull gitlab/gitlab-ee docker run --detach --hostname gitlab.example.com --publish 443:443 --publish 80:80 --publish 22:22 --name gitlab --restart always --volume /srv/gitlab/config:/etc/gitlab --volume /srv/gitlab/logs:/var/log/gitlab --volume /srv/gitlab/data:/var/opt/gitlab gitlab/gitlab-ee:latest
gitlab可以与ldap绑定,使用AD域账号进行登录。如果想要修改gitlab.rb文件,可以登入到容器中修改:
docker exec -it CONTAINER_ID /bin/bash
配置完成后,使用root访问 http://ip :
官方网站: https://docs.gitlab.com/omnibus/docker/
0×01 Git的传输协议了解
Git主要以两种方式跨越两个仓库传输数据。
1.哑协议
Git基于HTTP之上传输通常被称为哑协议,这是因为它在服务端不需要有针对Git特有的代码。这个获取过程仅仅是一系列GET请求,客户端可以假定服务端的Git仓库中的布局。简单解读官方给出的举例,一次git clone过程:
git clone http://github.com/schacon/simplegit-progit.git //下载simplegit-progit
Initialized empty Git repository in /private/tmp/simplegit-progit/.git/ //在/private/tmp/simplegit-progit/.git/目录中初始化一个空的git仓库
got ca82a6dff817ec66f44342007202690a93763949 //获取info/refs文件,这个文件由服务端的update-server-info生成,用于给不进行动态包生成的哑服务器提供辅助信息文件,以帮助客户机发现服务器有哪些引用和包,哑服务器意味着通过http访问
walk ca82a6dff817ec66f44342007202690a93763949 //获取commit对象
got 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 //查看commit对象的内容
Getting alternates list for http://github.com/schacon/simplegit-progit.git //获取替代仓库list
Getting pack list for http://github.com/schacon/simplegit-progit.git //获取打包文件list
Getting index for pack 816a9b2334da9953e530f27bcac22082a9f5b835 //获取这个打包文件的索引
Getting pack 816a9b2334da9953e530f27bcac22082a9f5b835 which contains cfda3bf379e4f8dba8717dee55aab78aef7f4daf //查看打包文件的索引是否包括要找的对象
walk 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 //获取commit
walk a11bef06a3f659402fe7563abf99ad00de2209e6 //下载对象
2.智能协议
HTTP方法是很简单但效率不是很高。使用智能协议是传送数据的更常用的方法。这些协议在远端都有Git智能型进程在服务,它可以读出本地数据并计算出客户端所需要的合适的数据给它,这有两类传输数据的进程:一对用于上传数据和一对用于下载。此处只对下载展开描述:
当下载数据时,fetch-pack和upload-pack进程就起作用了。客户端启动fetch-pack进程,连接至远端的upload-pack进程,以协商后续数据传输过程。在远端仓库有不同的方式启动upload-pack进程。你可以使用与receive-pack(接收推送到存储库中的内容时所启用的进程)相同的透过SSH管道的方式,也可以通过Git后台来启动这个进程,它默认监听在9418号端口上。这里fetch-pack进程在连接后像这样向后发送数据:
fgit-upload-pack schacon/simplegit-progit.git\0host=myserver.com\0
它也是以4字节指定后续字节长度的方式开始,然后是要运行的命令,和一个空字节,然后是服务端的主机名,再跟随一个最后的空字节。Git后台进程会检查这个命令是否可以运行,以及那个仓库是否存在,以及是否具有公开权限。如果所有检查都通过了,它会启动这个upload-pack进程并将客户端的请求移交给它。
如果你透过SSH使用获取功能,fetch-pack会像这样运行:
ssh -x git@github.com "git-upload-pack 'schacon/simplegit-progit.git'"
0×02 gitlab数据库结构了解
docker镜像使用的是postgresql数据库,一共有236张数据表,我们知道gitlab采用了ueba的用户权限管理模型,因此想要获得用户、项目、项目组、key之间的关系,我们首先要关心这几张表:
identities存储ldap的信息,其中extern_uid存储ldap的部门等信息 :
Column | Type |
---|---|
id | integer |
extern_uid | character varying |
provider | character varying |
user_id | integer |
created_at | timestamp without time zone |
updated_at | timestamp without time zone |
secondary_extern_uid | character varying |
saml_provider_id | integer |
keys存储key,以及与user_id的对应关系:
Column | Type |
---|---|
id | integer |
user_id | integer |
created_at | timestamp without time zone |
updated_at | timestamp without time zone |
key | text |
title | character varying |
type | character varying |
fingerprint | character varying |
public | boolean |
last_used_at | timestamp without time zone |
namespaces存储用户及项目组的路径,主要用于获取项目组(type=’Group’)的信息(description)
Column | Type |
---|---|
id | integer |
name | character varying |
path | character varying |
owner_id | integer |
created_at | timestamp without time zone |
updated_at | timestamp without time zone |
type | character varying |
description | character varying |
avatar | character varying |
membership_lock | boolean |
share_with_group_lock | boolean |
visibility_level | integer |
request_access_enabled | boolean |
ldap_sync_status | character varying |
ldap_sync_error | character varying |
ldap_sync_last_update_at | timestamp without time zone |
ldap_sync_last_successful_update_at | timestamp without time zone |
ldap_sync_last_sync_at | timestamp without time zone |
description_html | text |
lfs_enabled | boolean |
parent_id | integer |
shared_runners_minutes_limit | integer |
repository_size_limit | bigint |
require_two_factor_authentication | boolean |
two_factor_grace_period | integer |
cached_markdown_version | integer |
plan_id | integer |
project_creation_level | integer |
runners_token | character varying |
trial_ends_on | timestamp with time zone |
file_template_project_id | integer |
saml_discovery_token | character varying |
runners_token_encrypted | character varying |
custom_project_templates_group_id | integer |
auto_devops_enabled | boolean |
extra_shared_runners_minutes_limit | integer |
project_authorizations存储用户、项目以及访问权限的关系
Column | Type |
---|---|
user_id | integer |
project_id | integer |
access_level | integer |
其中,access_level的含义为:
10 => Guest access 20 => Reporter access 30 => Developer access 40 => Maintainer access 50 => Owner access # Only valid for groups
projects存储项目信息:
Column | Type |
---|---|
id | integer |
name | character varying(510) |
path | character varying(510) |
description | text |
created_at | timestamp with time zone |
updated_at | timestamp with time zone |
creator_id | integer |
namespace_id | integer |
last_activity_at | timestamp with time zone |
import_url | character varying(510) |
visibility_level | integer |
archived | boolean |
avatar | character varying(510) |
import_status | character varying(510) |
star_count | integer |
import_type | character varying(510) |
import_source | character varying(510) |
import_error | text |
ci_id | integer |
shared_runners_enabled | boolean |
runners_token | character varying |
build_coverage_regex | character varying |
build_allow_git_fetch | boolean |
build_timeout | integer |
pending_delete | boolean |
public_builds | boolean |
last_repository_check_failed | boolean |
last_repository_check_at | timestamp without time zone |
container_registry_enabled | boolean |
only_allow_merge_if_build_succeeds | boolean |
has_external_issue_tracker | boolean |
repository_storage | character varying |
request_access_enabled | boolean |
has_external_wiki | boolean |
lfs_enabled | boolean |
description_html | text |
only_allow_merge_if_all_discussions_are_resolved | boolean |
0×03 Gitlab日志了解
Gitlab初始化配置中,会在/var/log/gitlab目录下保存近1个月的日志,每天凌晨1点左右将目录下的*.log文件压缩为gz格式,比如将gitlab-shell.log压缩为gitlab-shell.log.1.gz,这个数字从1-30依次增加和轮换。
基于传输协议我们知道,当git执行一次git clone/git pull/git fetch的下载操作时,会在服务端启用<upload-pack>协议,gitlab本身没有提供直观的下载日志,因此我们需要通过这个协议的启动来进行gitlab的下载审计。
gitlab-shell.log: 此日志文件位于/var/log/gitlab/gitlab-shell中,该日志文件的作用是记录执行gitlab命令以及为项目添加ssh权限的日志文件:
time="2019-05-06T08:27:37+00:00" level=info msg="executing git command" command="gitaly-upload-pack unix:/var/opt/gitlab/gitaly/gitaly.socket {\"repository\":{\"storage_name\":\"default\",\"relative_path\":\"root/mytest.git\",\"git_object_directory\":\"\",\"git_alternate_object_directories\":[],\"gl_repository\":\"project-1\",\"gl_project_path\":\"root/mytest\"},\"gl_repository\":\"project-1\",\"gl_project_path\":\"root/mytest\",\"gl_id\":\"key-2\",\"gl_username\":\"root\",\"git_config_options\":[],\"git_protocol\":null}" pid=29421 user="user with id key-2"
更多其他日志的介绍可以浏览: https://docs.gitlab.com/ee/administration/logs.html
0×04 Gitlab代码下载以及权限审计
在了解了以上Gitlab的基础知识后,开始着手于对Gitlab的审计。首先我们讨论如何对代码下载进行审计。
gitlab-shell日志记录了upload pack 的操作,但是日志中并不直观,因此需要对日志处理,希望获取到json日志格式:
{ "time": "2019-05-06T08:27:37+00:00", "gitcommand": "git-upload-pack", "username": "test", "name": "测试账号", “user_department”: "运维部" "project_description": "用于gitlab测试", "gitpath": "/data/gitlab/git-data/repositories/root/mytest.git" ”key_id": "233", }
为了得到上方的日志信息,我们先从gitlab-shell.log日志中提取time、git command、gl_project_path、gl_id:
time="2019-05-06T08:27:37+00:00" git command="gitaly-upload-pack gl_project_path:"root/mytest" gl_id:"key-233"
由于日志中没有直接显示user的信息,因此需要从Gitlab的数据库users、keys、identities、namespaces表中查询:
通过key-id 获取user_id:
SELECT user_id FROM keys WHERE id=key-id
通过user_id获取name、username以及部门信息user_department:
SELECT name,username FROM users WHERE id=user_id SELECT extern_uid FROM identities WHERE user_id=usr_id
再从namespaces中查询path=’mytest’,以获取项目的描述信息project_description,用于与user_department进行比对。
SELECT description FROM projects where path=path
至此我们需要的信息就可以存为一条日志了,通过这种方法将gitlab-shell.log处理为可读性的json日志,再接入到ELK中用于审计。
通过 Python 可以再写一些告警规则,比如当用户所属部门与项目的描述不一致时,则发出邮件告警。也可以从数据库中获取其他的信息来补充日志。
在Gitlab数据库中,project_authorizations表记录用户、项目以及项目访问权限的关系:
user_id | project_id | access_level ---------+------------+-------------- 1 | 1 | 40
我们可以结合users和projects表,统计出可读的用户-项目访问权限表,以此来审计gitlab项目的访问权限,也可将这些用户对项目的访问权限加入到gitlab代码下载日志中去。
由于gitlab的数据库中包含了密钥这类重要敏感信息,因此gitlab的数据库建议绑定本地IP,笔者的做法是每天将仅需要使用到的数据推送到 MySQL 服务器中,再从MySQL服务器中获取对应信息。
推送users以及keys表:
#!/bin/bash psql -h /var/opt/gitlab/postgresql -d gitlabhq_production <<EOF COPY (SELECT id,user_id FROM keys) TO '/var/opt/gitlab/postgresql/key.csv' with csv header; COPY (SELECT id,name,username FROM users) TO '/var/opt/gitlab/postgresql/user.csv' with csv header; COPY (SELECT user_id,extern_uid FROM users) TO '/var/opt/gitlab/postgresql/department.csv' with csv header; EOF scp user.csv root@远程主机IP:/root scp key.csv root@ 远程主机IP :/root scp department.csv root@ 远程主机IP :/root
推送最新打包好的gitlab-shell.log.x.gz日志:
#!/bin/bash ls | find /var/log/gitlab/gitlab-shell/ -mtime -1 |grep gz |xargs -i cp -f {} /var/log/gitlab/gitlab-shell/gitlab-shell.log.gz scp -i /var/log/gitlab/gitlab-shell/.ssh/id_rsa gitlab-shell.log.gz root@远程主机IP:远程目录 sleep 10 rm -f gitlab-shell.log.gz
Python处理日志格式(部分代码):
import json import pymysql from datetime import datetime def get_info(key_id): conn = pymysql.connect( host = 'x.x.x.x', port = 3306, user = 'gitlab', password = 'password', database = 'gitlab' ) cursor = conn.cursor() #get user_id sql = "SELECT user_id FROM keys WHERE id=" + str(key_id) cursor.execute(sql) row_1 = cursor.fetchone() if row_1 != None: user_id = row_1[0] #get name_username sql2 = "SELECT name,username FROM users WHERE id=" + str(user_id) cursor.execute(sql2) row_2 = cursor.fetchone() name_username = row_2 #get user_department sql3 = "SELECT extern_uid FROM identities WHERE id=" + str(user_id) cursor.execute(sql3) row_3 = cursor.fetchone() if row_3 != None: userdepartment = row_3[0].split(",")[1] else: userdepartment = 'null' user_department = userdepartment else: name_username = {'null','null' return (name_username,user_department) def logtojson(): with open(r'gitlab-shell.log') as myfile: logs = myfile.readlines() array = [] for log in logs: array.append(log) logdict = [] for i in range(len(array)): info = array[i] info1 = info.split() if info1[0] == "I," and info1[6] == "gitlab-shell:": time1 = info1[1].split("[")[1] time = time1.split(".")[0] gitcommand = info1[10].split("<")[1] gitpath = info1[11].split(">")[0] key = info1[16].split("-")[1] key_id = key.split(".")[0] group = gitpath.split("/")[5] info = get_info(key_id) name = info[0][0] username = info[0][1] user_department = info[1] newlog = { "logDate": time, "gitcommand":gitcommand, "gitpath":gitpath, "name":name, "username":username, "user_department":user_department, "key_id":key_id } logdict.append(newlog) with open(datetime.now().date().isoformat()+'.log',"w") as f: for i in logdict: json.dump(i,f,ensure_ascii=False) f.write('\n') if __name__ == '__main__': logtojson()
以上就是gitlab下载及权限审计,欢迎各位大佬指教。
*本文原创作者:胡说,本文属于FreeBuf原创奖励计划,未经许可禁止转载
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