CVE-2019-6637 in BIG-IP ASM
Summary
by MITRE
On BIG-IP (ASM) 14.1.0-14.1.0.5, 14.0.0-14.0.0.4, 13.0.0-13.1.1.4, and 12.1.0-12.1.4, Application logic abuse of ASM REST endpoints can lead to instability of BIG-IP system. Exploitation of this issue causes excessive memory consumption which results in the Linux kernel triggering OOM killer on arbitrary processes. The attack requires an authenticated user with role of "Guest" or greater privilege. Note: "No Access" cannot login so technically it's a role but a user with this access role cannot perform the attack.
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Analysis
by VulDB Data Team • 10/17/2023
The vulnerability identified as CVE-2019-6637 represents a critical application logic flaw within F5 BIG-IP Application Security Manager (ASM) REST API endpoints. This security weakness affects multiple versions of the BIG-IP platform including versions 12.1.0 through 12.1.4, 13.0.0 through 13.1.1.4, 14.0.0 through 14.0.0.4, and 14.1.0 through 14.1.0.5. The flaw manifests as an improper handling of application logic within the REST interface, specifically targeting the ASM module which is responsible for web application security protection. The vulnerability is categorized under CWE-284 which describes improper access control, and aligns with ATT&CK technique T1210 for exploiting known vulnerabilities in network devices. The attack vector requires authentication with at least Guest privileges, making it particularly concerning as it can be exploited by users who have minimal access rights but can still cause significant system instability.
The technical exploitation of this vulnerability results in a memory exhaustion condition that ultimately triggers the Linux kernel's Out-Of-Memory (OOM) killer mechanism. This occurs when an authenticated user with Guest or higher privileges makes specific requests to the ASM REST endpoints that cause excessive memory allocation within the BIG-IP system. The application logic abuse leads to a gradual consumption of available system memory resources until the kernel is forced to terminate arbitrary processes to prevent system crash. The OOM killer intervention represents a defensive mechanism within the Linux kernel that automatically terminates processes when memory pressure becomes critical, but this behavior effectively constitutes a denial of service condition that compromises system stability. The vulnerability demonstrates a classic example of resource exhaustion attacks that can be leveraged to disrupt normal system operations without requiring administrative privileges.
The operational impact of CVE-2019-6637 extends beyond simple service disruption to potentially compromising the overall reliability and availability of critical network infrastructure. When the OOM killer terminates processes, it can affect not only the ASM functionality but also other critical system components that depend on the available memory resources. This instability can lead to unpredictable behavior in security monitoring, traffic management, and application delivery services that rely on the BIG-IP platform. The vulnerability's requirement for only Guest-level access makes it particularly dangerous as it can be exploited by users who have legitimate access to the system for monitoring or administrative purposes but who may not be authorized to perform such destructive actions. This aspect of the vulnerability creates a significant risk for organizations where access control policies may not adequately restrict user privileges, potentially allowing malicious actors to escalate their impact through legitimate access channels.
Mitigation strategies for CVE-2019-6637 should focus on both immediate remediation and long-term access control improvements. Organizations should prioritize applying the vendor-provided security patches and updates that address this specific vulnerability, as these fixes typically involve proper input validation and memory management within the ASM REST endpoints. Additionally, implementing strict role-based access controls is essential to prevent unauthorized users from accessing the affected REST API endpoints. The principle of least privilege should be enforced where users with Guest access should not be granted unnecessary permissions that could enable exploitation of such vulnerabilities. Network segmentation and monitoring of REST API access patterns can help detect anomalous behavior that might indicate exploitation attempts. Security teams should also consider implementing automated alerting mechanisms that monitor for unusual memory consumption patterns or OOM killer activity, as these indicators can serve as early warning signs of potential exploitation attempts. The vulnerability serves as a reminder of the importance of proper application logic validation and resource management in enterprise security platforms, particularly those handling sensitive network traffic and application security functions.