GitHub security researcher Kevin Backhouse has recently discovered a seven-year-old critical Linux privilege escalation bug in the polkit system service, which was previously called PoilcyKit, which could allow any hackers to bypass authorization to gain root access on the affected system.
If you don’t know the work of polkit, then let me justify it in short; it’s a toolkit, and if an application needs root privileges for a task, then polkit asks for the appropriate or relevant password.
The recently discovered bug has been tracked as, CVE-2021-3560 and it’s mainly found in polkit service that is actually associated with a typical Linux system and service manager component, “systemd.”
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Seven-year-old Polkit Flaw
This vulnerability was integrated into Commit bfa5036b which was introduced seven years ago, and this bug explored several paths in various Linux distributions since it’s initially directed in polkit version 0.113.
- CVE ID: CVE-2021-3560
- CVSS v3 Base Score: 7.8
- Attack Vector: Local
- Privileges Required: Low
- User Interaction: None
- Integrity Impact: High
This bug requires only a few commands using the terminal tools like bash, kill, and dbus-send, in short, this bug is easy to exploit.
By starting a dbus-send command this bug could be triggered, but, when polkit is still in the midst of concocting the request, it kills it. When polkit asks for the UID of a connection that doesn’t exist, an error arises due to the execution of this during the midst of an authentication request.
Vulnerable Distributions
Here’s the list of all the distribution that are vulnerable to this bug:-
- RHEL 8: Yes
- Fedora 21 (or later): Yes
- Debian testing (“bullseye”): Yes
- Ubuntu 20.04: Yes
Exploitation
Kevin Backhouse notes that this bug is a possible privilege escalation that was very easy and quick to execute and with only a few commands it can be exploited.
Here, the query that had already ended incorrectly the polkit handles it. Instead of canceling the process, Polkit feigned that the request had come from a process with the UID 0.
This implies that here in this stage the Polkit simply assumes this process request arrived from a root process, and it immediately approves the request. Though this didn’t always work perfectly, but still it is frequently enough to keep the effort low.
Mitigation
According to the Red Hat report, currently, there are no such proper mitigations are available, if any available then they don’t need the criteria of Red Hat Product Security.
However, to remediate any possible risk that may emerge due to this bug, the experts have strongly recommended every user to immediately update their Linux installations as soon as possible.
