CVE-2017-3203 in Spring-flex
Summary
by MITRE
The Java implementations of AMF3 deserializers in Pivotal/Spring Spring-flex derive class instances from java.io.Externalizable rather than the AMF3 specification's recommendation of flash.utils.IExternalizable. A remote attacker with the ability to spoof or control an RMI server connection may be able to send serialized Java objects that execute arbitrary code when deserialized.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability CVE-2017-3203 represents a critical security flaw in the Java implementations of AMF3 deserializers within Pivotal/Spring Spring-flex libraries. This issue stems from a fundamental deviation from the established AMF3 specification requirements, creating a dangerous discrepancy between expected and actual behavior in serialized object handling. The vulnerability specifically affects systems that utilize Spring-flex for remote method invocation and object serialization, making it particularly concerning for enterprise applications that rely on these components for communication between client and server.
The technical flaw manifests in how the deserialization process handles class instances during object reconstruction. According to the AMF3 specification, objects should derive from flash.utils.IExternalizable to ensure proper serialization and deserialization behavior. However, the Pivotal/Spring implementation incorrectly implements this by deriving from java.io.Externalizable instead. This deviation creates a dangerous execution path where maliciously crafted serialized objects can exploit the difference in how these two interfaces handle object state management during deserialization. The vulnerability operates at the core of Java's serialization mechanism, leveraging the inherent trust placed in serialized objects during the deserialization phase.
The operational impact of this vulnerability extends far beyond simple code execution, as it enables remote code execution through carefully crafted serialized objects that can be transmitted over RMI connections. An attacker with the ability to spoof or control an RMI server connection can leverage this flaw to inject malicious serialized objects that will execute arbitrary code on the target system when processed by the vulnerable deserializer. This creates a significant attack surface for remote exploitation, particularly in environments where RMI services are exposed to untrusted networks or where authentication mechanisms may be bypassed. The vulnerability essentially transforms the deserialization process from a safe data reconstruction mechanism into a potential code execution vector.
The security implications of CVE-2017-3203 align with CWE-502, which addresses deserialization of untrusted data, and can be mapped to ATT&CK technique T1059.007 for remote code execution through serialized objects. Organizations using affected Spring-flex versions face significant risk of unauthorized system compromise, data exfiltration, and potential lateral movement within their network infrastructure. The vulnerability's exploitation requires minimal privileges beyond network access to the RMI endpoints, making it particularly dangerous in environments with insufficient network segmentation or monitoring controls. Remediation efforts must include immediate patching of affected Spring-flex libraries, implementation of network controls to restrict RMI access, and comprehensive code reviews to identify other potential deserialization vulnerabilities within the application stack.