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https://issues.apache.org/jira/browse/LOG4J2-3425?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Volkan Yazici closed LOG4J2-3425.
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Resolution: Fixed
> Syslog appender lacks the SocketOptions setting
> -----------------------------------------------
>
> Key: LOG4J2-3425
> URL: https://issues.apache.org/jira/browse/LOG4J2-3425
> Project: Log4j 2
> Issue Type: Improvement
> Components: Appenders
> Affects Versions: 2.12.1
> Reporter: Jiří Smolík
> Priority: Major
> Fix For: 2.18.0
>
>
> Recently, we've had an issue with our syslog server (collector), where it was
> suddenly unable to forward messages sent to it. This resulted in flooding the
> server and ultimately, exhausting its resources (memory and allocated
> temporary storage).
> However, more interestingly, Log4j2 appender behaved as follows:
> # At the moment of exhaustion, one thread (T1) entered the synchronized
> block in TcpSocketManager (see
> https://github.com/apache/logging-log4j2/blob/e2ee2f4dd9327eb1841023c3269ba12f5673e694/log4j-core/src/main/java/org/apache/logging/log4j/core/net/TcpSocketManager.java#L217)
> and tried to write the message (see
> [https://github.com/apache/logging-log4j2/blob/e2ee2f4dd9327eb1841023c3269ba12f5673e694/log4j-core/src/main/java/org/apache/logging/log4j/core/net/TcpSocketManager.java#L253]).
> # The server didn't respond immediately - actually, it blocked T1 for hours
> (it was most likely waiting for resources to be free).
> # In the meantime, all threads attempting to write a message to the syslog
> appender hanged at the synchronized block (they were waiting for T1 to
> finish).
> Eventually, the connection to the server broke apart or some resources were
> freed, and T1 finished. Interestingly, it didn't throw any exception, but
> that is beside the point in this issue.
> So, what happened is that the server got flooded and blocked one thread in
> our application, but due to the way TcpSocketManager is implemented, our
> application suffered a DoS.
> As a precaution to such dreadful scenario, I would like to request adding a
> read timeout setting to the TcpSocketManager (also syslog appender), which
> would in case of the above described situation prevent T1 from blocking other
> threads for a long time. At least, that's my idea of an easy fix. Connect and
> reconnect timeout settings have a different purpose and were useless in this
> case.
> I am aware that the issue is also a matter of the syslog server
> configuration, but application developers do not always have it under their
> control.
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