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https://issues.apache.org/jira/browse/LOG4J2-3279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17470540#comment-17470540
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sumeet sharma commented on LOG4J2-3279:
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Thanks, [~rgoers].
Just to summarize, We can take alternate mitigation strategies for the short
term until we can upgrade.
In the meanwhile, we should be mindful of the caveat you mentioned and to avoid
infinite lookup in the message part, we either need to set the system property
_*log4j2.formatMsgNoLookups*_ or use the _*{nolookups}*_ option on the %m
converter in the PatternLayout.
> 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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