CVE-2021-21290

Netty is an open-source, asynchronous event-driven network application
framework for rapid development of maintainable high performance protocol
servers & clients. In Netty before version 4.1.59.Final there is a
vulnerability on Unix-like systems involving an insecure temp file. When
netty’s multipart decoders are used local information disclosure can occur
via the local system temporary directory if temporary storing uploads on
the disk is enabled. On unix-like systems, the temporary directory is
shared between all user. As such, writing to this directory using APIs that
do not explicitly set the file/directory permissions can lead to
information disclosure. Of note, this does not impact modern MacOS
Operating Systems. The method “File.createTempFile” on unix-like systems
creates a random file, but, by default will create this file with the
permissions “-rw-r–r–”. Thus, if sensitive information is written to this
file, other local users can read this information. This is the case in
netty’s “AbstractDiskHttpData” is vulnerable. This has been fixed in
version 4.1.59.Final. As a workaround, one may specify your own
“java.io.tmpdir” when you start the JVM or use
“DefaultHttpDataFactory.setBaseDir(…)” to set the directory to something
that is only readable by the current user.