Scala 2.13.x before 2.13.9 has a Java deserialization chain in its JAR file. On its own, it cannot be exploited. There is only a risk in conjunction with Java object deserialization within an application. In such situations, it allows attackers to erase contents of arbitrary files, make network connections, or possibly run arbitrary code (specifically, Function0 functions) via a gadget chain.

The compilation daemon in Scala before 2.10.7, 2.11.x before 2.11.12, and 2.12.x before 2.12.4 uses weak permissions for private files in /tmp/scala-devel/${USER:shared}/scalac-compile-server-port, which allows local users to write to arbitrary class files and consequently gain privileges.