CVE-2020-5234 in MessagePack for C#
Summary
by MITRE
MessagePack for C# and Unity before version 1.9.3 and 2.1.80 has a vulnerability where untrusted data can lead to DoS attack due to hash collisions and stack overflow. Review the linked GitHub Security Advisory for more information and remediation steps.
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Analysis
by VulDB Data Team • 03/27/2024
The vulnerability identified as CVE-2020-5234 affects MessagePack implementations for both C# and Unity platforms, specifically versions prior to 1.9.3 and 2.1.80 respectively. This issue represents a critical security flaw that stems from inadequate handling of serialized data structures during deserialization processes. The vulnerability manifests when applications process untrusted input through MessagePack serialization libraries, creating conditions where maliciously crafted payloads can trigger denial of service attacks through systematic exploitation of hash collision mechanisms.
The technical root cause of this vulnerability lies in the MessagePack library's insufficient protection against hash collision attacks during the deserialization phase. When untrusted data is processed, the library's internal hash table implementation becomes vulnerable to algorithmic complexity attacks where attackers can craft input data that deliberately causes hash collisions. This leads to a degradation of performance from O(1) to O(n) complexity for hash operations, and in extreme cases can cause stack overflow conditions when the library attempts to handle these collisions through recursive or deeply nested operations. The vulnerability operates at the intersection of improper input validation and inadequate resource management within the serialization framework, creating a pathway for attackers to consume excessive system resources through carefully constructed message payloads.
From an operational perspective, this vulnerability presents a significant risk to applications that rely on MessagePack for data serialization, particularly those processing external or user-provided data streams. The attack surface is broad as MessagePack is widely used across various applications including web services, game engines, and distributed systems where data exchange occurs between untrusted parties. Successful exploitation can result in complete system unavailability, requiring system restarts and potentially leading to cascading failures in dependent services. The impact extends beyond simple resource exhaustion to potentially compromise the availability of critical business applications and services that depend on stable serialization infrastructure.
The vulnerability aligns with CWE-400, which addresses "Uncontrolled Resource Consumption" and specifically targets the improper handling of hash table operations in serialization libraries. Additionally, this weakness maps to ATT&CK technique T1499.004, "Endpoint Denial of Service," where adversaries exploit application-level vulnerabilities to consume system resources and cause service disruption. Organizations should implement immediate mitigations including upgrading to patched versions of the MessagePack libraries, implementing input validation and sanitization measures, and deploying rate limiting and resource monitoring controls. The remediation process requires careful attention to application compatibility, as upgrading may introduce breaking changes in serialization formats and require thorough testing of data exchange processes across the entire application ecosystem.