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https://issues.apache.org/jira/browse/LOG4J2-3279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17470230#comment-17470230
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Ralph Goers commented on LOG4J2-3279:
-------------------------------------
The infinite recursion happens when a user passes an infinitely recursive
lookup string in an HTTP header (for example) and you store that in a
ThreadContext variable which you then reference in something evaluated as part
of event processing - such as the Route on a routing appender. If you know you
aren't putting unverified data into ThreadContext variables that are then
referenced in the configuration when processing logging events then you are not
subject to the problem - with one caveat.
The original security report - CVE-2021-44228 allowed lookups to be processed
when they appeared in the data being logged. To avoid that you either need to
set the system property or use the \{nolookups} option on the %m converter in
the PatternLayout. However, you will noticed that in the history section of two
of the CVEs it is called out that these mitigations are insufficient. They do
work for the vast majority of logging but if you have code that uses
logger.printf(), or uses one of the alternate MessageFactories then those
events are not blocked from processing lookups. If you are 100% sure your code
doesn't have anything but vanilla format strings (for example if you use SLF4J
you cannot have anything else) then this mitigation would work. If you are
unsure you MUST upgrade.
To be clear, the only solution the Log4j team can really recommend is to
upgrade to 2.3.2, 2.12.4 or 2.17.1 to be absolutely sure as well as to be in
compliance with things like
https://techcrunch.com/2022/01/05/ftc-legal-action-log4j/.
> Alternative mitigation documented for CVE-2021-45105 doesn't work for
> messages without context lookup if the Log4J2 consumers are not on version >=
> 2.15
> --------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: LOG4J2-3279
> URL: https://issues.apache.org/jira/browse/LOG4J2-3279
> Project: Log4j 2
> Issue Type: Bug
> Components: Documentation
> Affects Versions: 2.14.0
> Reporter: sumeet sharma
> Priority: Major
>
> Alternative mitigation documented for CVE-2021-45105 doesn't work for
> messages without context lookup if the Log4J2 consumers are not on version >=
> 2.15.
> Official mitigation provided in
> [https://logging.apache.org/log4j/2.x/security.html] reads:
> h3.
> "[CVE-2021-45105|https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-45105]:
> Apache Log4j2 does not always protect from infinite recursion in lookup
> evaluation
> h3. <trimmed for brevity>
> h3. Mitigation
> h4. Log4j 1.x mitigation
> Log4j 1.x is not impacted by this vulnerability.
> h4. Log4j 2.x mitigation
> Upgrade to Log4j 2.3.1 (for Java 6), 2.12.3 (for Java 7), or 2.17.0 (for Java
> 8 and later).
> *Alternatively, this infinite recursion issue can be mitigated in
> configuration:*
> * *In PatternLayout in the logging configuration, replace Context Lookups
> like ${ctx:loginId} or $${ctx:loginId} with Thread Context Map patterns (%X,
> %mdc, or %MDC).*
> * *Otherwise, in the configuration, remove references to Context Lookups
> like ${ctx:loginId} or $${ctx:loginId} where they originate from sources
> external to the application such as HTTP headers or user input."*
> The alternative mitigation statement seems to be making assumptions.
> The infinite recursion issue in the message part of the log seems to be fixed
> in version 2.15. Versions prior to that (I tried on 2.14.0), this issue is
> still applicable. **
> Assuming a user is on Log4J 2.14.0, if they follow this mitigation step by
> step, they will still be able to reproduce infinite recursion issue.
> pom.xml
> {code:java}
> <dependencies>
> <dependency>
> <groupId>org.apache.logging.log4j</groupId>
> <artifactId>log4j-api</artifactId>
> <version>2.14.0</version>
> </dependency>
> <dependency>
> <groupId>org.apache.logging.log4j</groupId>
> <artifactId>log4j-core</artifactId>
> <version>2.14.0</version>
> </dependency>
> </dependencies> {code}
> Code:
> {code:java}
> LOG.info("Problematic payload {}", "${${::${::$${::-j}}}}");
> LOG.info("Problematic payload ${${::${::$${::-j}}}}");{code}
>
> Log4j2.xml
> {code:java}
> <Console name="Console" target="SYSTEM_OUT">
> <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level
> %logger{36} - %m%n"/>
> </Console>{code}
>
> Output
> {code:java}
> 2021-12-23 14:40:49,031 main ERROR An exception occurred processing Appender
> Application java.lang.IllegalStateException: Infinite loop in property
> interpolation of ::-${::-$${::-j}}: : {code}
>
> If this stands true, then the documentation should mention:
> * either the minimum required version
> * or usage of -Dlog4j2.formatMsgNoLookups=true for the alternative
> mitigation to work.
>
> I've only kept 2.14.0 as the affected version as I tested on same but this
> might be applicable to quite a few versions.
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