On January 26, NSFOCUS CERT detected that the Qualys research team publicly disclosed a privilege escalation vulnerability (CVE-2021-4034) found in Polkit’s pkexec, also known as PwnKit. The vulnerability is due to the inability of pkexec to properly process the call parameters, thereby executing the environment variable as a command. An attacker with arbitrary user rights can exploit this vulnerability by modifying the environment variable in the default configuration, thereby gaining root privileges on the affected host. At present, the details and PoC of the vulnerability have been disclosed, and relevant users are requested to take measures to protect them as soon as possible.
Polkit (PolicyKit) is an application-level tool set in Unix-like systems. It implements communication between processes with different priorities by defining and auditing permission rules. pkexec, part of the Polkit open source application framework, enables authorized unprivileged users to execute commands as privileged users according to defined policies.
NSFOCUS has successfully reproduced it immediately:
Reference link: https://www.qualys.com/2022/01/25/cve-2021-4034/pwnkit.txt
Scope of Impact
All Polkit versions released from May 2009 to present.
Note: Polkit is pre-installed on CentOS, Ubuntu, Debian, Redhat, Fedora, Gentoo, Mageia and other Linux distributions, and all Linux systems with Polkit are affected.
- CentOS 6: polkit-0.96-11.el6_10.2
- CentOS 7: polkit-0.112-26.el7_9.1
- CentOS 8.0: polkit-0.115-13.el8_5.1
- CentOS 8.2: polkit-0.115-11.el8_2.2
- CentOS 8.4: polkit-0.115-11.el8_4.2
- Ubuntu 14.04 ESM: policykit-1-0.105-4ubuntu3.14.04.6+esm1
- Ubuntu 16.04 ESM: policykit-1-0.105-14.1ubuntu0.5+esm1
- Ubuntu 18.04 LTS: policykit-1-0.105-20ubuntu0.18.04.6
- Ubuntu 20.04 LTS: policykit-1-0.105-26ubuntu1.2
- Ubuntu 21.10: policykit-1-0.105-31ubuntu0.1
- Debain stretch: policykit-1 0.105-18+deb9u2
- Debain buster: policykit-1 0.105-25+deb10u1
- Debain bullseye: policykit-1 0.105-31+deb11u1
- Debain bookworm,bullseye: policykit-1 0.105-31.1
Linux system users can check whether the current system is affected by checking the Polkit version. The commands for mainstream Linux distributions are as follows:
rpm -qa polkit
rpm -qa polkit
1. At present, the official patch has been released to fix this vulnerability. It is recommended that affected users install it in time for protection.
Download link: https://gitlab.freedesktop.org/polkit/polkit/-/commit/a2bf5c9c83b6ae46cbd5c779d3055bff81ded683
2. At present, all mainstream Linux distributions have released security patches or updated versions to fix this vulnerability. It is recommended that users install the patch as soon as possible or refer to official measures for protection:
|Linux distribution version||Official Notice|
Note: For Linux distributions such as CentOS, Ubuntu, Debian, etc. that use a package manager to update Polkit, you can directly run the following commands to update and repair:
yum clean all && yum makecache
yum update polkit -y
sudo apt-get update
sudo apt-get install policykit-1
apt upgrade policykit-1
If the operating system used by the affected users has not yet released a fix, or the patch update cannot be installed temporarily, the following measures can be used for temporary protection without affecting the business.
Execute the following system command to remove the suid bit of pkexec:
chmod 0755 /usr/bin/pkexec
This advisory is only used to describe a potential risk. NSFOCUS does not provide any commitment or promise on this advisory. NSFOCUS and the author will not bear any liability for any direct and/or indirect consequences and losses caused by transmitting and/or using this advisory. NSFOCUS reserves all the rights to modify and interpret this advisory. Please include this statement paragraph when reproducing or transferring this advisory. Do not modify this advisory, add/delete any information to/from it, or use this advisory for commercial purposes without permission from NSFOCUS.
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