CVE-2020-5933 in BIG-IP
Summary
by MITRE • 10/30/2020
On versions 15.1.0-15.1.0.5, 14.1.0-14.1.2.3, 13.1.0-13.1.3.4, 12.1.0-12.1.5.1, and 11.6.1-11.6.5.1, when a BIG-IP system that has a virtual server configured with an HTTP compression profile processes compressed HTTP message payloads that require deflation, a Slowloris-style attack can trigger an out-of-memory condition on the BIG-IP system.
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Analysis
by VulDB Data Team • 11/30/2020
The vulnerability described in CVE-2020-5933 represents a critical resource exhaustion issue affecting F5 BIG-IP systems running specific versions of their software stack. This flaw manifests when the system processes HTTP compressed content through virtual servers configured with HTTP compression profiles, creating a condition where maliciously crafted compressed payloads can trigger memory allocation exhaustion. The vulnerability operates at the application layer and specifically targets the decompression mechanisms within the BIG-IP system's HTTP processing pipeline, making it particularly dangerous for systems handling high volumes of web traffic. The attack vector leverages Slowloris-style techniques, which are characterized by maintaining multiple connections open for extended periods while sending minimal data, thereby consuming system resources progressively. This vulnerability affects multiple major release versions including 15.1.x, 14.1.x, 13.1.x, 12.1.x, and 11.6.x, indicating a widespread impact across the F5 BIG-IP product line and suggesting a fundamental flaw in the compression handling logic rather than a localized issue.
The technical implementation of this vulnerability stems from inadequate resource management during HTTP decompression operations within the BIG-IP system's processing engine. When the system encounters compressed HTTP payloads that require deflation, it allocates memory buffers to handle the decompression process. However, the implementation fails to properly limit or monitor the memory consumption during this process, particularly when dealing with malformed or maliciously crafted compressed data. The vulnerability specifically targets the deflate decompression algorithm and occurs when the system processes compressed content that requires progressive memory allocation. This creates a scenario where an attacker can maintain multiple concurrent connections, each sending compressed data that requires substantial memory for decompression, leading to progressive memory exhaustion. The flaw aligns with CWE-400, which covers "Uncontrolled Resource Consumption," and more specifically with CWE-770, "Allocation of Resources Without Limits or Throttling," demonstrating poor resource management practices in the decompression handling code.
The operational impact of CVE-2020-5933 extends beyond simple system performance degradation to potentially causing complete system outages and service disruption. When the memory exhaustion occurs, it can lead to the BIG-IP system becoming unresponsive or crashing entirely, resulting in denial of service for all services relying on that system. This vulnerability is particularly concerning for critical infrastructure environments where availability is paramount, as it can be exploited with relatively simple attack tools and requires minimal resources to execute. The attack can be executed by a single attacker or multiple attackers simultaneously, making it difficult to defend against through traditional network monitoring approaches. Organizations using affected BIG-IP versions may experience cascading failures, as the system's inability to process new requests can affect downstream services and applications. The vulnerability also impacts the system's ability to maintain existing connections, potentially causing connection timeouts and session disruptions for legitimate users. This type of attack falls under the ATT&CK technique T1499.004, "Endpoint Denial of Service," and specifically relates to resource exhaustion attacks that target application-level processing capabilities.
Mitigation strategies for CVE-2020-5933 require immediate implementation of both temporary workarounds and permanent fixes through official F5 security patches. Organizations should apply the latest security updates from F5 as soon as possible, as these patches contain fixes for the resource management issues in the HTTP decompression handling code. Temporary mitigations include implementing rate limiting on HTTP compression requests, disabling HTTP compression profiles on virtual servers when possible, and configuring connection limits to prevent the accumulation of long-lived connections. Network-level protections can be implemented through firewalls and intrusion detection systems to monitor for suspicious patterns of compressed HTTP traffic that may indicate exploitation attempts. Additionally, implementing proper monitoring and alerting for memory usage on BIG-IP systems can help detect exploitation attempts before they cause complete system failures. Organizations should also consider implementing web application firewalls that can filter out malformed compressed content before it reaches the BIG-IP system. The vulnerability highlights the importance of proper input validation and resource management in application security, as it demonstrates how seemingly benign functionality can become a vector for critical system compromise. Regular security assessments and vulnerability scanning should include checks for this specific vulnerability across all BIG-IP deployments to ensure comprehensive protection against this class of resource exhaustion attacks.