Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

Summary

The "ExtensionLoader.instantiateExtension(Class, String)" method loads a class by its fully-qualified name via "Class.forName()" and invokes its no-arg constructor, with the class name sourced from the "manifest.propertiesentry" of a model archive. The existing "isAssignableFromcheck" correctly rejects classes that are not subtypes of the expected extension interface (BaseToolFactoryfor factory=, ArtifactSerializerfor serializer-class-*), but the check runs "afterClass.forName()" has already loaded and initialized the named class. "Class.forName()" with default initialization semantics executes the target class's static initializer before returning, so an attacker who can supply a crafted model archive can cause the static initializer of any class on the classpath to run during model loading, regardless of whether that class passes the subsequent type check. Exploitation requires a class with attacker-useful side effects in its static initializer (for example, JNDI lookup, outbound network I/O, or filesystem access) to be present on the classpath, so this is not a drop-in remote code execution; however, the attack surface grows as third-party model distribution becomes more common (community model repositories, Hugging Face-style sharing), where users routinely load model files from origins they do not control. A secondary, narrower vector affects deployments that ship legitimate BaseToolFactoryor ArtifactSerializersubclasses with side-effecting no-arg constructors: a malicious manifest can name such a class and force its constructor to run during model load. Mitigation: * 2.x users should upgrade to 2.5.9. * 3.x users should upgrade to 3.0.0-M3. Note: The fix introduces a package-prefix allowlist that is consulted before Class.forName()is invoked, so the static initializer of a disallowed class is never executed. Classes under the opennlp.prefix remain permitted by default. Deployments that load models referencing factories or serializers outside opennlp.*must opt those packages in, either programmatically via ExtensionLoader.registerAllowedPackage(String)before the first model load, or by setting the OPENNLP_EXT_ALLOWED_PACKAGESsystem property to a comma-separated list of allowed package prefixes. Users who cannot upgrade immediately should ensure that all model files are sourced from trusted originsand should audit their classpath for classes with side-effecting static initializers or constructors, particularly any that perform JNDI lookups, network requests, or filesystem operations during class initialization. All versions prior to 2.5.9 and 3.x prior to 3.0.0-M3 are affected.