Second, while the method has been tested on various configurations and systems, it is possible that it won’t work on all and could result in crashes on some. This means the immunization needs to be reapplied if the server is restarted. First, the fix is transient because the changes the exploit makes apply to the running Java process and will be reverted when the JVM restarts. It’s important to understand that using this has some significant caveats. Using the exploit against itself could be a viable short-term solution. One use case for something like this are all those third-party vendor products - packaged applications, embedded devices and appliances - that don’t have patches available yet or vulnerable products that have reached end-of-life and will never receive an official update. Researchers from security firm Cybereason developed such an immunization exploit and researchers from LunaSec further improved it and hosted it on a live server as a public service. It’s possible to leverage the vulnerability itself on affected servers to make certain changes to the live system and application that would prevent further exploitation. Exploiting the flaw itself to temporarily prevent exploitation Ephemeral containers are supported in Kubernetes v1.16 and later. The agent is available on GitHub and can also be deployed as an ephemeral container to an existing Kubernetes pod to patch applications that are already running in other containers. Zip -q -d log4j-core-*.jar org/apache/logging/log4j/core/lookup/JndiLookup.class Since Java components are essentially ZIP archives, administrators can run the following command to modify and patch a vulnerable package instance: However, this can also be achieved by essentially ripping out the entire JndiLookup class, which implements this functionality, from an affected Log4j package. One way to fix the vulnerability is to disable the use of JNDI message lookups, which is what Log4j 2.16.0 does. The original exploit used LDAP (Lightweight Directory Access Protocol), which is the most common one, but others are also supported: DNS (Domain Name System), RMI (Remote Method Invocation), NDS (Novell Directory Services), NIS (Network Information Service), and CORBA (Common Object Request Broker Architecture). JNDI can be used to load such objects from remote naming services over several protocols. This vulnerability is caused by the way Log4j uses a Java feature called JNDI (Java Naming and Directory Interface) that was designed to allow the loading of additional Java objects during runtime execution. Like with most vulnerabilities, alternative mitigations are very useful for security teams, but it’s important to understand their limitations and the false sense of security some of them can induce. Packaged products from third-party vendors might contain vulnerable versions of the popular logging library that users can’t modify without updating the whole product, so they are dependent on vendors to release updates.īusiness critical servers and applications might not be able to restart immediately or applications might run in containers for which new container images must be built. Unfortunately, immediate patching is not viable in all scenarios. Updating the affected component to the latest version - currently 2.17.0 for Java 8 and newer - is the best way to mitigate the flaws identified so far: CVE-2021-44228, also known as Log4Shell, which leads to remote code execution, CVE-2021-45046, and CVE-2021-45105, which can cause denial-of-service conditions. Since the flaw was first disclosed and attackers started exploiting it, security researchers have discovered additional security issues in Log4j and various ways to bypass some of the proposed mitigations, leaving security teams scrambling for the correct ways to protect their applications, servers and networks. The IT security community has been hard at work for the past week to investigate a critical and easy-to-exploit vulnerability in a hugely popular Java component called Log4j that’s present in millions of applications and products.
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