CVE-2020-11995 in Dubbo
Summary
by MITRE • 01/11/2021
A deserialization vulnerability existed in dubbo 2.7.5 and its earlier versions, which could lead to malicious code execution. Most Dubbo users use Hessian2 as the default serialization/deserialization protool, during Hessian2 deserializing the HashMap object, some functions in the classes stored in HasMap will be executed after a series of program calls, however, those special functions may cause remote command execution. For example, the hashCode() function of the EqualsBean class in rome-1.7.0.jar will cause the remotely load malicious classes and execute malicious code by constructing a malicious request. This issue was fixed in Apache Dubbo 2.6.9 and 2.7.8.
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Analysis
by VulDB Data Team • 02/11/2021
The CVE-2020-11995 vulnerability represents a critical deserialization flaw in Apache Dubbo versions 2.7.5 and earlier, exposing systems to remote code execution attacks through improper handling of serialized data. This vulnerability specifically affects the Hessian2 serialization protocol that Dubbo uses by default, creating a dangerous attack surface where malicious payloads can be executed during the deserialization process. The flaw stems from how Hessian2 processes HashMap objects during deserialization, where it triggers execution of methods stored within the map's constituent classes. This behavior creates an execution chain that can be exploited by attackers to run arbitrary code on vulnerable systems. The vulnerability is particularly concerning because it leverages the common practice of using Hessian2 as the primary serialization mechanism in Dubbo-based applications, making it a widespread risk across numerous enterprise deployments.
The technical exploitation of this vulnerability occurs through the manipulation of the hashCode() method execution within specific classes during deserialization. When Hessian2 deserializes a HashMap, it iterates through the map's contents and invokes methods on the stored objects. The attack vector specifically targets the EqualsBean class found in the rome-1.7.0.jar library, where the hashCode() method is designed to load and execute remote classes. This design flaw allows attackers to construct malicious serialized requests that, when processed by the vulnerable Dubbo service, trigger remote code execution. The exploitation chain typically involves creating a serialized payload that, when deserialized, causes the EqualsBean's hashCode() method to load a malicious class from a remote server, effectively executing arbitrary code on the target system. This type of vulnerability aligns with CWE-502, which describes deserialization of untrusted data as a critical security weakness.
The operational impact of CVE-2020-11995 extends beyond simple remote code execution, as it represents a severe threat to enterprise security infrastructure. Organizations using Dubbo versions prior to 2.6.9 or 2.7.8 face significant risk of unauthorized access, data breaches, and system compromise. The vulnerability's exploitation does not require authentication, making it particularly dangerous for services exposed to untrusted networks or the internet. Attackers can leverage this flaw to establish persistent backdoors, escalate privileges, or use the compromised system as a launch point for further attacks within the network. The widespread adoption of Dubbo in microservices architectures means that a single vulnerable service can potentially compromise entire application ecosystems. This vulnerability also aligns with ATT&CK technique T1059.007, which covers scripting languages, as the malicious code execution can involve various scripting mechanisms during the remote class loading process.
Organizations should immediately implement mitigation strategies to address this vulnerability, starting with upgrading to Dubbo versions 2.6.9 or 2.7.8 where the issue has been resolved. The fix typically involves modifying the deserialization process to prevent execution of methods during object reconstruction, particularly focusing on the handling of HashMap objects and their constituent classes. Security teams should also implement network segmentation to limit exposure of Dubbo services to untrusted networks, while monitoring for suspicious deserialization activity. Additional protective measures include validating all incoming serialized data, implementing strict access controls, and considering the use of alternative serialization protocols that do not exhibit similar vulnerabilities. Regular security assessments and penetration testing should be conducted to identify other potential deserialization vulnerabilities in the broader application stack. The remediation process should also include updating dependencies such as rome-1.7.0.jar to versions that do not contain the vulnerable EqualsBean class, ensuring comprehensive protection against similar exploitation vectors.