Log4Shell: RCE 0-day exploit found in log4j2, a popular Java logging package, hugely popular

A few hours ago, a 0-day exploit in the popular Java logging library log4j2 was discovered that results in Remote Code Execution (RCE) by logging a certain string.

Given how ubiquitous this library is, the impact of the exploit (full server control), and how easy it is to exploit, the impact of this vulnerability is quite severe. We’re calling it “Log4Shell” for short.

The 0-day was tweeted along with a POC posted on GitHub. Since this vulnerability is still very new, there isn’t a CVE to track it yet. This has been published as CVE-2021-44228.

This post provides resources to help you understand the vulnerability and how to mitigate it for yourself.

Who is impacted?​

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.

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

Many Open Source projects like the Minecraft server, Paper, have already begun patching their usage of log4j2.

Simply changing an iPhone’s name has been shown to trigger the vulnerability in Apple’s servers.

Updates (3 hours after posting): According to this blog post (see translation), JDK versions greater than 6u211, 7u201, 8u191, and 11.0.1 are not affected by the LDAP attack vector. In these versions com.sun.jndi.ldap.object.trustURLCodebase is set to false meaning JNDI cannot load remote code using LDAP.

However, there are other attack vectors targeting this vulnerability which can result in RCE. An attacker could still leverage existing code on the server to execute a payload. An attack targeting the class org.apache.naming.factory.BeanFactory, present on Apache Tomcat servers, is discussed in this blog post.

Affected Apache log4j2 Versions​

2.0 <= Apache log4j <= 2.14.1

Permanent Mitigation​

Version 2.15.0 of log4j has been released without the vulnerability. log4j-core.jar is available on Maven Central here, with [release notes] and [log4j security announcements].

The release can also be downloaded from the Apache Log4j Download page.

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Source: Log4Shell: RCE 0-day exploit found in log4j2, a popular Java logging package | LunaSec

You can find sites that have been exloited https://github.com/YfryTchsGD/Log4jAttackSurface

Robin Edgar

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