All about Log4j

What is the use of Log4j in Java?

Log4j is a fast, reliable and flexible logging framework which is written in java. It is an open-source logging API for java. Simply the logging means some way to indicate the state of the system at runtime.

What is Log4j?

log4j is a reliable, fast and flexible logging framework (APIs) written in Java, which is distributed under the Apache Software License. log4j is a popular logging package written in Java. log4j has been ported to the C, C++, C#, Perl, Python, Ruby, and Eiffel languages.

Is Log4j outdated?

Apache Log4j is a very old logging framework and was the most popular one for several years. It introduced basic concepts, like hierarchical log levels and loggers, that are still used by modern logging frameworks. The development team announced Log4j’s end of life in 2015.

What apps use Log4j?

Apache log4j 2 is widely used in many popular software applications, such as Apache Struts, ElasticSearch, Redis, Kafka and others. While supplying an easy and flexible user experience, Apache log4j 2 has historically been vulnerable to process and deserialize user inputs.siku 2 zilizopita

What is the purpose of logging?

The purpose of logging is to track error reporting and related data in a centralized way. Logging should be used in big applications and it can be put to use in smaller apps, especially if they provide a crucial function.

What is a logging framework used for?

A logging framework is a utility specifically designed to standardize the process of logging in your application. This can come in the form of a third party tool, such as log4j or its .

Why is Log4j important?

log4j is a tool to help the programmer output log statements to a variety of output targets. In case of problems with an application, it is helpful to enable logging so that the problem can be located. With log4j it is possible to enable logging at runtime without modifying the application binary.

Who developed Log4j?

Apache Software Foundation

What is the basic thing in Log4j?

Log4j has three main components: loggers, appenders, and layouts. Loggers are named destinations that capture log messages and send them to appenders. Appenders deliver log messages to their destinations, such as files, sockets, or consoles. Layouts are used to define the formatting of log messages.

Which is better Logback or Log4j?

Key Difference Between Log4j vs Logback Better versions: When we compare versions of log4j and logback, then log4j is better than logback versions less than 1.2. 1. As logback is improved, version log4j and versions log4j2 and logback have no difference in terms of performance or any features.

What can I use instead of Log4j?

SLF4J, Logback, Logstash, Loki, and Bunyan are the most popular alternatives and competitors to Log4j.

What is difference between Log4j and Log4j2?

Community support: Log4j 1. x is not actively maintained, whereas Log4j 2 has an active community where questions are answered, features are added and bugs are fixed. Automatically reload its configuration upon modification without losing log events while reconfiguring.

What is Log4j vulnerability?

The vulnerability allows for unauthenticated remote code execution. Log4j 2 is an open source Java logging library developed by the Apache Foundation. Log4j 2 is widely used in many applications and is present, as a dependency, in many services. These include enterprise applications as well as numerous cloud services.saa 14 zilizopita

Is Log4j 1 vulnerable?

The version 1 branch of Log4J is vulnerable to other RCE attacks and should be updated.siku 1 iliyopita

How is Log4j exploited?

Exploitation can be achieved by a single string of text, which can trigger an application to reach out to a malicious external host if it is logged via the vulnerable instance of Log4j, effectively granting the adversary the ability to retrieve a payload from a remote server and execute it locally.siku 1 iliyopita

Who is affected

  • Impact: arbitrary code execution as the user the parent process is running as (code fetched from the public Internet, or lolbins already present on system, or just fetching shared secrets or environment variables and returning them to the attacker)
  • Targets: Servers and clients that run Java and also log anything using the log4j framework – primarily a server-side concern, but any vulnerable endpoint could be a target or a pivot point
  • Downstream projects: until proven otherwise, assume anything that includes log4j – including Elasticsearch, Apache Struts / Solr / Druid / Flink, etc. – is affected in a way that requires mitigation; see below
  • Affected versions: log4j 2.x confirmed – log4j 1.x only indirectly (previous information disclosure vulns) (in some configurations)
  • Appliances: Don’t forget appliances that may be using Java server components, but won’t be detected by unauthenticated vulnerability scanning
  • Log forwarding: logging infrastructure often has many “northbound” (send my logs to someone) and “southbound” (receiving logs from someone) forwarding/relaying topologies. Chaining them together for exploitation must also be considered.
  • Cloud: Multiple large providers also affected (but this guide focuses mostly on customer-managed side)
  • Misnomers: No, it is not also called LogJam. That name is already taken. (Initial LunaSec post used that name, then picked a new one once they found out.)


Technical analysis


Direct remediation:

Mitigations – easiest

  • (@MalwareTechBlog): If you can’t upgrade log4j, you can mitigate the RCE vulnerability by setting log4j2.formatMsgNoLookups to True (-Dlog4j2.formatMsgNoLookups=true in JVM command line) (but only for >= 2.10.0).
  • Putting Cloudflare in front of your site (and terminating your SSL there) could be an easy but only partial solution

Mitigations – official project itself (

  • Users of Log4j 2.10 or greater may add -Dlog4j2.formatMsgNoLookups=true as a command line option or add log4j2.formatMsgNoLookups=true to a file on the classpath to prevent lookups in log event message.
  • Users since Log4j 2.7 may specify %m{nolookups} in the PatternLayout configuration to prevent lookups in log event message
  • Remove the JndiLookup and JndiManager classes from the log4j-core jar. Removal of the JndiManager will cause the JndiContextSelector and JMSAppender to no longer function

Mitigations – harder

Mitigations – ecosystem

Affected (and unaffected) products

Note: this list focuses primarily on customer-controlled components. For fully cloud-based components, top section of the YfryTchsGD repo is pretty good as a starting point.

Disclaimer: caching/summaries is best effort and may be out of date or incorrect – always validate for yourself

Claimed patched (previously vulnerable, now remediated/mitigated or updates available)

Confirmed affected – version differences, workarounds suggested, status pending, or not yet analyzed

  • Apache Struts (LunaSec ref only, need better link)
  • Apache James SMTP Server – Twitter PoC (@dlitchfield)
  • Apereo CAS and community workarounds
  • Forescout – unconfirmed – KB 12049 (support wall); mixed; newer versions patches available, older have patches still pending; others unaffected; see also blog post
  • ManageEngine (ADManager Plus) – commmunity post, official reply, patch as caution
  • neo4j (community official post, 4.2+ affected, workaround, patched release pending)
  • OpenMRS (suggests -D workaround, patched release pending)
  • PEGA (remediation via SQL cmd for on prem and self-managed)
  • Rosette – only RNI WebServices (deprecated product) – “vulnerability will be removed”
  • Powerschool (Reddit only, appears exploitable, official pending)
  • SAFE FME Server – not vulnerable, updating 2.x to 2.15 anyway, but also not providing patches for unsupported versions
  • SDL WorldServer affected, workarounds listed
  • Seafile – Pro only, Elastic search dependency, workarounds listed, risk “low”
  • Silver Peak GMS Orchestrator (Aruba/HPE) – no patch yet, workarounds listed
  • Tosca – licensing server uses Elasticsearch, claimed OK but patch also pending; Java Engine patch pending

Claimed unaffected / not vulnerable (no action taken or required)

Claimed unaffected by default (but configurable to be affected if user opted for log4j or added extensions)

Multi-product – vulnerable, mixed, or not yet fully determined

Potentially affected (circumstantial use of log4j or behind support wall)

Not yet determined, non-commital, or mixed/controversial

  • Apache Kafka claimed unaffected, but this pull request seems to show otherwise
  • Blender (original claimed PoC was apparently a joke)
  • DocuSign (“patching or mitigating as vulnerable configurations are identified”)
  • Elastic – claimed no RCE in Elasticsearch, but an info disclosure vuln was patched, but this community thread is mixed (2021-12-11 23:49 UTC). Elastic Cloud on Kubernetes requires mitigations. Other components/offerings listed as unaffected.
  • Flexera / Revenera (placeholder / in progress – 2021-12-13 02:56 UTC)
  • Mathematica (community forum only, not definitive)
  • Nextcloud (no Java per GitHub issue, but replies indicate potential for otherwise)
  • Untangle (community forum only, no authoritative answer 2021-12-13 04:21)

Indirect / integration known (can relay/forward/integrate, but no default dependency)

Other rollup lists


Finding potentially vulnerable software

Detecting exploitation attempts

Vulnerability scanning and testing

Multi-layered defense stacks and guides


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