On January 25, 2022, Qualys announced the discovery of a local privilege escalation vulnerability that it identified as PwnKit. The PwnKit vulnerability affects PolicyKit’s pkexec, a SUID-root program installed by default on many Linux distributions. The same day of the announcement, a proof of concept (PoC) exploit was built and published by the security research community.

A new advisory from Qualys discloses a local privilege escalation bug in SUID-set program ‘pkexec’. The flaw has been designated the CVE ID of CVE-2021-4034 and nicknamed “pwnkit” by the vulnerability finders. The CVSSv3 base score is calculated to be a high 7.8 out of 10.0. The vulnerable program is a part of Polkit, which manages process privileges.

During an investigation of a malware campaign, I discovered that multiple emails were bypassing a specific email security system. Interestingly, there were no bypass techniques used. Instead, the flood of spear-phishing emails made the email security system allow some of the emails, at which point I began my research on Microsoft Outlook. The issue in this case was that the specially crafted malicious link parsing on the security system was weak.

Since 2009, more than 12 years ago, all major Linux distributions have been incorporating a high severity security hole that remained unnoticed until just recently. The vulnerability and exploit, dubbed “PwnKit” (CVE-2021-4034), uses the vulnerable “pkexec” tool, and allows a local user to gain root system privileges on the affected host. Polkit (formerly PolicyKit) is a component for controlling system-wide privileges in Unix-like operating systems.

“Crowdsourced security provides a way for security teams to expand their efficiency, especially when it comes to managing their external attack surface,” said Rickard Carlsson, Co-founder and CEO of Detectify. “Hackers have eyes and ears all over the web, and they’re constantly monitoring attack surfaces for exploitable entry points.

The Trustwave Threat Hunting team has authored a practical guide to help the cybersecurity community address the Linux “polkit” Local Privilege Escalation vulnerability (CVE-2021-4034) by identifying common behavior in exploitation.