CVE-2017-7957 in Notes
Summary
by MITRE
XStream through 1.4.9, when a certain denyTypes workaround is not used, mishandles attempts to create an instance of the primitive type 'void' during unmarshalling, leading to a remote application crash, as demonstrated by an xstream.fromXML("") call.
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Analysis
by VulDB Data Team • 05/23/2025
The vulnerability identified as CVE-2017-7957 represents a critical security flaw in the XStream Java library that affects versions through 1.4.9. This issue arises from improper handling of primitive type instantiation during the unmarshalling process, specifically when the library encounters attempts to create instances of the primitive type 'void'. The vulnerability is particularly concerning because it can be exploited remotely, allowing attackers to cause application crashes without requiring any special privileges or authentication. The flaw manifests when XStream processes XML input that contains constructs attempting to instantiate primitive types, leading to unexpected behavior in the deserialization pipeline. Security researchers have identified that this vulnerability can be triggered through a simple xstream.fromXML("") call, demonstrating how easily an attacker can exploit the flaw to disrupt application functionality.
The technical root cause of CVE-2017-7957 stems from XStream's insufficient validation and handling of primitive type instantiation during object deserialization. When the library processes XML input containing attempts to create instances of primitive types such as 'void', it fails to properly validate these requests, leading to a crash condition in the application. This behavior is categorized under CWE-248, which addresses "Uncaught Exception" conditions in software systems. The vulnerability specifically exploits the library's inability to handle edge cases in its type resolution mechanism, where primitive types are not properly filtered or rejected during the unmarshalling process. The flaw is particularly dangerous because it can be triggered by malformed XML input that does not necessarily contain malicious payloads, but rather exploits the library's handling of legitimate edge cases in type instantiation.
From an operational impact perspective, CVE-2017-7957 poses significant risks to applications that rely on XStream for XML processing and object deserialization. The vulnerability can be leveraged to perform denial-of-service attacks against applications, causing them to crash and become unavailable to legitimate users. This makes the flaw particularly attractive to attackers seeking to disrupt services or gain unauthorized access to systems. The impact extends beyond simple application crashes, as it can be used as a stepping stone for more sophisticated attacks or to mask other malicious activities. The vulnerability affects any system that processes untrusted XML input through XStream, including web applications, middleware components, and enterprise systems that handle external data feeds. Organizations using affected versions of XStream may experience service interruptions, data processing failures, and potential system instability when encountering maliciously crafted XML input.
Mitigation strategies for CVE-2017-7957 focus on implementing proper input validation and library updates to address the underlying vulnerability. The most effective approach involves upgrading to XStream version 1.4.10 or later, where the issue has been resolved through enhanced type validation and proper handling of primitive type instantiation. Organizations should also implement the denyTypes workaround recommended by the XStream maintainers, which involves explicitly configuring the library to reject dangerous types during deserialization. Additionally, security teams should deploy input validation measures that filter or sanitize XML input before processing, particularly when dealing with untrusted data sources. The remediation process should include comprehensive testing to ensure that the fixes do not introduce regressions in application functionality while maintaining security. Organizations should also consider implementing network-level protections such as firewalls and intrusion detection systems to monitor for suspicious XML processing patterns that may indicate exploitation attempts. This vulnerability highlights the importance of proper input validation and the need for security-conscious development practices when handling object deserialization in enterprise applications.