New zero-day exploit for Log4j Java library is an enterprise nightmare

Proof-of-concept exploits for a critical zero-day vulnerability in the ubiquitous Apache Log4j Java-based logging library are currently being shared online, exposing home users and enterprises alike to ongoing remote code execution attacks.

Log4j is developed by the Apache Foundation and is widely used by both enterprise apps and cloud services.

Thus, while home users might have moved away from Java (although popular games like Minecraft still use it), anything from enterprise software to web apps and products from Apple, Amazon, Cloudflare, Twitter, and Steam is likely vulnerable to RCE exploits targeting this vulnerability.

Ongoing scans, exploitation of vulnerable systems

The bug, now tracked as CVE-2021-44228 and dubbed Log4Shell, is an unauthenticated RCE vulnerability allowing complete system takeover on systems with Log4j 2.0-beta9 up to 2.14.1.

It was reported by Alibaba Cloud's security team to Apache on November 24. They also revealed that CVE-2021-44228 impacts default configurations of multiple Apache frameworks, including Apache Struts2, Apache Solr, Apache Druid, Apache Flink, and others.

After the first proof-of-concept exploit was published on GitHub yesterday, threat actors began scanning the Internet [1, 2] for systems vulnerable to this remotely exploitable security flaw that doesn't require authentication.

Additionally, CERT NZ (New Zealand's national Computer Emergency Response Team) has issued a security advisory warning of active exploitation in the wild (also confirmed by Coalition Director Of Engineering - Security Tiago Henriques and security expert Kevin Beaumont).

Nextron Systems' Head of Research Florian Roth has shared a set of YARA rules for detecting CVE-2021-44228 exploitation attempts.

Mass scanning activity detected from multiple hosts checking for servers using Apache Log4j (Java logging library) vulnerable to remote code execution (https://t.co/GgksMUlf94).

Query our API for "tags=CVE-2021-44228" for source IP addresses and other IOCs. #threatintel

— Bad Packets (@bad_packets) December 10, 2021

Patch and mitigation available

Apache has released Log4j 2.15.0 to address the maximum severity CVE-2021-44228 RCE vulnerability.

The flaw can also be mitigated in previous releases (2.10 and later) by setting system property "log4j2.formatMsgNoLookups" to "true" or removing the JndiLookup class from the classpath.

Those using the library are advised to upgrade to the latest release ASAP seeing that attackers are already searching for exploitable targets.

"Similarly to other high-profile vulnerabilities such as Heartbleed and Shellshock, we believe there will be an increasing number of vulnerable products discovered in the weeks to come," the Randori Attack Team said today.

"Due to the ease of exploitation and the breadth of applicability, we suspect ransomware actors to begin leveraging this vulnerability immediately."

Security companyLunasec also underscored the severity of attacks using CVE-2021-44228 RCE exploits.

"Many, many services are vulnerable to this exploit. Cloud services like Steam, Apple iCloud, and apps like Minecraft have already been found to be vulnerable," Lunasec said.

"Anybody using Apache Struts is likely vulnerable. We've seen similar vulnerabilities exploited before in breaches like the 2017 Equifax data breach."

Friday evening, researchers from cybersecurity firm Cybereason released a 'vaccine' package called Logout4Shell that exploits a remote vulnerable Log4j server to change a setting that mitigates the vulnerability.

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Update December 10, 11:46 AM EST: Cloudflare told BleepingComputer that its systems are not vulnerable to CVE-2021-44228 exploitation attempts.

"We responded quickly to evaluate all potential areas of risk and updated our software to prevent attacks, and have not been able to replicate any external claims that we might be at risk," said Leigh Ann Acosta, Cloudflare's Director of Public Relations.

Update December 10, 9:39 PM EST: Added information about vaccine.