CVE-2018-5541 in BIG-IP ASM
Summary
by MITRE
When F5 BIG-IP ASM 13.0.0-13.1.0.1, 12.1.0-12.1.3.5, 11.6.0-11.6.3.1, or 11.5.1-11.5.6 is processing HTTP requests, an unusually large number of parameters can cause excessive CPU usage in the BIG-IP ASM bd process.
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Analysis
by VulDB Data Team • 04/25/2023
The vulnerability described in CVE-2018-5541 represents a significant denial of service weakness within F5 BIG-IP Application Security Manager (ASM) implementations. This flaw specifically targets versions spanning multiple release branches including 13.0.0 through 13.1.0.1, 12.1.0 through 12.1.3.5, 11.6.0 through 11.6.3.1, and 11.5.1 through 11.5.6. The vulnerability manifests when the system processes HTTP requests containing an unusually high number of parameters, leading to disproportionate CPU consumption in the BIG-IP ASM bd process. This issue falls under the category of resource exhaustion attacks where malicious actors can exploit the system's handling of parameter-heavy requests to consume excessive computational resources.
The technical mechanism behind this vulnerability involves the BIG-IP ASM module's inadequate handling of HTTP request parameters during the parsing and processing phases. When the system encounters requests with an unusually large number of parameters, the bd process responsible for application security monitoring and enforcement begins to consume excessive CPU cycles. This occurs because the processing algorithm does not properly implement bounds checking or parameter limiting mechanisms, allowing the system to allocate resources in a manner that scales linearly with parameter count rather than maintaining a reasonable resource ceiling. The vulnerability specifically impacts the backend processing component of ASM, which is designed to inspect and enforce security policies on application traffic, making it a critical component for maintaining service availability.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially compromising the availability of critical application services. When the bd process consumes excessive CPU resources, it can lead to complete service disruption as the system becomes unable to process legitimate requests effectively. This creates a scenario where attackers can perform denial of service attacks by simply crafting HTTP requests with numerous parameters, causing the application security manager to become unresponsive. The vulnerability affects organizations that rely on F5 BIG-IP ASM for web application protection, potentially exposing their applications to prolonged outages and service disruptions. The impact is particularly severe in high-traffic environments where the system's ability to handle concurrent requests is already strained, making such attacks more effective and damaging.
Organizations affected by this vulnerability should implement immediate mitigations including applying the latest F5 security patches and updates released to address this specific issue. Network administrators should also consider implementing parameter limits and request rate limiting at the perimeter to prevent the exploitation of this vulnerability. The mitigation strategy should include monitoring for unusual parameter counts in HTTP requests and implementing automated response mechanisms to block or quarantine suspicious traffic patterns. Additionally, organizations should review their current ASM configuration to ensure proper resource allocation and consider implementing additional load balancing mechanisms to distribute traffic more effectively. This vulnerability aligns with attack patterns documented in the MITRE ATT&CK framework under the denial of service category, specifically targeting system resource exhaustion techniques that can be leveraged to disrupt service availability. The weakness can be classified as a CWE-770 (Allocation of Resources Without Limits or Throttling) which directly relates to the improper handling of parameter counts leading to unbounded resource consumption.