CVE-2018-20168 in gVisor
Summary
by MITRE
Google gVisor before 2018-08-22 reuses a pagetable in a different level with the paging-structure cache intact, which allows attackers to cause a denial of service ("physical address not valid" panic) via a crafted application.
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Analysis
by VulDB Data Team • 04/21/2020
The vulnerability identified as CVE-2018-20168 resides within Google gVisor, a container sandboxing solution designed to provide strong isolation between containerized applications and the host system. This flaw represents a critical issue in the memory management subsystem of gVisor, specifically concerning how the system handles page table structures during memory operations. The vulnerability manifests when the system reuses page table entries at different levels while maintaining the paging-structure cache, creating a scenario where memory access validation fails catastrophically. This behavior directly violates fundamental memory safety principles that are essential for containerized environments where isolation is paramount.
The technical implementation of this vulnerability stems from improper handling of page table reuse mechanisms within gVisor's memory management layer. When the system processes memory operations, it maintains a cache of paging structures to improve performance. However, the flaw occurs when page table entries are recycled at different hierarchical levels without properly clearing or invalidating the cached structures. This creates a condition where the memory subsystem attempts to translate virtual addresses using stale cache entries, resulting in a "physical address not valid" panic. The underlying cause aligns with CWE-129, which addresses improper handling of memory access validation, and demonstrates poor memory management practices that compromise system stability.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it fundamentally undermines the reliability and security guarantees that gVisor provides to containerized applications. Attackers can exploit this weakness by crafting malicious applications that specifically target the memory management subsystem, triggering the panic condition and causing the entire gVisor instance to crash. This creates a denial of service scenario that affects not only the targeted container but potentially the entire host system if multiple containers are running. The vulnerability particularly impacts environments where gVisor is used for security-sensitive workloads, as it provides an attack vector that could be leveraged to disrupt critical services or potentially escalate privileges through system instability.
Mitigation strategies for CVE-2018-20168 require immediate patching of gVisor installations to version 2018-08-22 or later, which contains the necessary fixes to properly handle page table reuse scenarios. Organizations should implement comprehensive monitoring of gVisor instances for panic conditions and ensure that proper logging mechanisms are in place to detect potential exploitation attempts. Additionally, system administrators should consider implementing additional security controls such as runtime application whitelisting and memory access monitoring to detect anomalous behavior patterns that might indicate exploitation attempts. From an ATT&CK perspective, this vulnerability maps to T1499.004 (Endpoint Denial of Service) and T1059.001 (Command and Scripting Interpreter), as attackers could potentially use this weakness to disrupt system availability while maintaining persistence through crafted applications. The fix addresses the root cause by ensuring proper cache invalidation when page table structures are reused at different levels, preventing the propagation of stale memory translation entries that lead to the panic condition.