CVE-2019-25076 in Open vSwitch
Summary
by MITRE • 09/09/2022
The TSS (Tuple Space Search) algorithm in Open vSwitch 2.x through 2.17.2 and 3.0.0 allows remote attackers to cause a denial of service (delays of legitimate traffic) via crafted packet data that requires excessive evaluation time within the packet classification algorithm for the MegaFlow cache, aka a Tuple Space Explosion (TSE) attack.
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Analysis
by VulDB Data Team • 10/14/2022
The vulnerability identified as CVE-2019-25076 represents a significant denial of service weakness within Open vSwitch implementations that affect versions 2.x through 2.17.2 and 3.0.0. This flaw specifically targets the Tuple Space Search algorithm which forms the core of packet classification mechanisms within the software. The issue manifests when remote attackers submit specially crafted packet data that triggers excessive computational overhead during the MegaFlow cache evaluation process, resulting in substantial delays for legitimate network traffic. The attack exploits fundamental design characteristics of the TSS algorithm that were not adequately protected against adversarial input patterns that can cause exponential growth in processing requirements.
The technical implementation of this vulnerability stems from the inherent complexity of the Tuple Space Search algorithm's evaluation process within Open vSwitch's packet classification framework. When legitimate packets are processed through the system, the algorithm must evaluate numerous tuple combinations to determine appropriate flow matching rules. Under normal circumstances, this process remains efficient and predictable. However, when attackers construct packet data that forces the system to evaluate an exponentially growing number of tuple combinations, the algorithm becomes computationally overwhelmed. This creates a scenario where the MegaFlow cache, which should provide performance optimization through caching previously computed results, actually becomes a point of failure rather than a performance enhancer. The vulnerability operates at the intersection of algorithmic complexity and network processing efficiency, where malicious input can cause legitimate traffic processing to become arbitrarily delayed.
The operational impact of CVE-2019-25076 extends far beyond simple service disruption, creating substantial risks for network infrastructure that relies on Open vSwitch implementations. Organizations utilizing affected versions of Open vSwitch face potential network degradation where legitimate traffic experiences significant delays that can effectively render network services unusable. The attack does not necessarily require complete system compromise or data exfiltration, making it particularly dangerous as it can be executed remotely without elevated privileges. Network administrators may observe gradual performance degradation followed by complete service unavailability as the system becomes overwhelmed by the computational demands of the crafted packet sequences. This vulnerability particularly affects virtualized network environments where Open vSwitch serves as the primary packet processing engine, potentially impacting cloud computing platforms, software-defined networking deployments, and network function virtualization implementations.
Mitigation strategies for CVE-2019-25076 should address both immediate defensive measures and long-term architectural improvements to prevent exploitation. Organizations should prioritize upgrading to patched versions of Open vSwitch where available, as version 2.17.3 and 3.0.1 contain specific fixes that limit the computational complexity of the Tuple Space Search algorithm. Network administrators should implement rate limiting mechanisms and packet filtering rules that can identify and block suspicious packet patterns before they reach the vulnerable classification engine. Additionally, monitoring systems should be enhanced to detect unusual processing delays or cache evaluation patterns that may indicate an active TSE attack. The implementation of input validation and normalization routines can help prevent malformed packets from entering the critical processing paths. From a security architecture perspective, this vulnerability highlights the importance of applying principle of least privilege and defense in depth strategies, ensuring that even if one component is compromised, the overall network infrastructure maintains operational integrity. This issue aligns with CWE-770, which addresses allocation of resources without limits or with inadequate limits, and represents a classic example of resource exhaustion attacks that fall under ATT&CK technique T1499.004 for Network Denial of Service. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of successful exploitation attempts.