Virtual Event Today: Supply Chain Security Summit - Join Event In-Progress

Security Experts:

Connect with us

Hi, what are you looking for?



CISA Tells Organizations to Patch Linux Kernel Vulnerability Exploited by Malware

The US Cybersecurity and Infrastructure Security Agency (CISA) on Thursday added a Linux kernel flaw to its Known Exploited Vulnerabilities Catalog and instructed federal agencies to address it within three weeks.

The US Cybersecurity and Infrastructure Security Agency (CISA) on Thursday added a Linux kernel flaw to its Known Exploited Vulnerabilities Catalog and instructed federal agencies to address it within three weeks.

The vulnerability is tracked as CVE-2021-3493 and it’s related to the OverlayFS file system implementation in the Linux kernel. It allows an unprivileged local user to gain root privileges, but it only appears to affect Ubuntu.

CVE-2021-3493 has been exploited in the wild by a stealthy Linux malware named Shikitega, which researchers at AT&T Alien Labs detailed in early September. Shikitega is designed to target endpoints and IoT devices running Linux, allowing the attacker to gain full control of the system. It has also been used to download a cryptocurrency miner onto the infected device.

As part of the malware’s infection chain, two Linux vulnerabilities are exploited for privilege escalation: CVE-2021-3493 and CVE-2021-4034.

CVE-2021-4034 is named PwnKit and it impacts Polkit’s Pkexec, a SUID-root program found in all Linux distributions. CISA warned about this vulnerability being exploited in attacks in June. Cisco mentioned exploitation in a recent report describing a Chinese attack framework and its associated RAT, which targets Windows, Linux, and macOS systems.

The news reports published when Shikitega’s existence came to light focused on the malware itself and did not highlight the fact that this appeared to be the first known instance of CVE-2021-3493 being exploited for malicious purposes.

Technical details and proof-of-concept (PoC) exploits for this vulnerability are publicly available.

CISA has now added the flaw to its Known Exploited Vulnerabilities Catalog and has instructed federal agencies to patch their systems until November 10. While federal agencies are required by a binding operational directive to fix these flaws, CISA strongly urges all organizations to prioritize patching for vulnerabilities listed in its catalog.

In addition, CISA has added a recent Zimbra vulnerability to the catalog. The security hole was only patched after exploitation began.

*updated to clarify that only Ununtu is affected by CVE-2021-3493

Related: CISA Clarifies Criteria for Adding Vulnerabilities to ‘Must Patch’ List

Related: CISA’s ‘Must Patch’ List Puts Spotlight on Vulnerability Management Processes

Related: CISA: Vulnerability in ​​Delta Electronics ICS Software Exploited in Attacks

Written By

Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.

Click to comment

Daily Briefing Newsletter

Subscribe to the SecurityWeek Email Briefing to stay informed on the latest threats, trends, and technology, along with insightful columns from industry experts.

Join this webinar to learn best practices that organizations can use to improve both their resilience to new threats and their response times to incidents.


Join this live webinar as we explore the potential security threats that can arise when third parties are granted access to a sensitive data or systems.


Expert Insights

Related Content


Zendesk is informing customers about a data breach that started with an SMS phishing campaign targeting the company’s employees.


Less than a week after announcing that it would suspended service indefinitely due to a conflict with an (at the time) unnamed security researcher...


The release of OpenAI’s ChatGPT in late 2022 has demonstrated the potential of AI for both good and bad.


Satellite TV giant Dish Network confirmed that a recent outage was the result of a cyberattack and admitted that data was stolen.


The changing nature of what we still generally call ransomware will continue through 2023, driven by three primary conditions.

Application Security

PayPal is alerting roughly 35,000 individuals that their accounts have been targeted in a credential stuffing campaign.


No one combatting cybercrime knows everything, but everyone in the battle has some intelligence to contribute to the larger knowledge base.


A recently disclosed vBulletin vulnerability, which had a zero-day status for roughly two days last week, was exploited in a hacker attack targeting the...