sumeet sharma created LOG4J2-3279:
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Summary: 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
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}
{code}
*LOG.info("Problematic payload {}", "${${::-${::-$${::-j}}}}");
LOG.info("Problematic payload ${${::-${::-$${::-j}}}}");*
Log4j2.xml
{code:java}
{code}
*<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d\{HH:mm:ss.SSS} [%t] %-5level
%logger\{36} - %m%n"/>
</Console>*
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 the minimum required
version 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 a quite a few versions.
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