CVE-2020-24371 in Lua
Summary
by MITRE
lgc.c in Lua 5.4.0 mishandles the interaction between barriers and the sweep phase, leading to a memory access violation involving collectgarbage.
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Analysis
by VulDB Data Team • 08/18/2020
The vulnerability identified as CVE-2020-24371 resides within the Lua 5.4.0 implementation, specifically in the lgc.c file which governs the garbage collection mechanism. This flaw represents a critical memory safety issue that manifests during the interaction between the garbage collection barriers and the sweep phase of the Lua runtime environment. The Lua programming language employs a mark-and-sweep garbage collector to manage memory automatically, and this particular vulnerability exploits a race condition or improper state handling during the transition between different garbage collection phases.
The technical root cause involves the mishandling of memory barriers during the sweep phase of garbage collection. In Lua's garbage collector, barriers serve as mechanisms to maintain consistency between the mark and sweep phases by ensuring that objects referenced during marking are properly accounted for during sweeping. When the collectgarbage function is invoked, the system transitions through multiple states including marking and sweeping phases. The flaw occurs when the interaction between these barriers and the sweep phase creates an inconsistent memory state, potentially leading to dangling pointers or invalid memory accesses. This vulnerability specifically affects the lgc.c implementation which manages the garbage collection logic and memory management operations within the Lua interpreter.
The operational impact of this vulnerability is severe as it can result in memory access violations that may cause application crashes or potentially enable memory corruption attacks. When the garbage collection process encounters this condition, the system may attempt to access memory locations that have already been freed or are otherwise invalid, leading to segmentation faults or undefined behavior. Attackers could potentially exploit this vulnerability by crafting specific input sequences that trigger the problematic garbage collection path, possibly leading to denial of service conditions or in more sophisticated scenarios, arbitrary code execution depending on the memory layout and surrounding system conditions. The vulnerability affects any application that utilizes Lua 5.4.0 and invokes the collectgarbage function during runtime operations.
Mitigation strategies for this vulnerability primarily involve upgrading to a patched version of Lua where the garbage collection interaction has been corrected. System administrators should prioritize updating their Lua installations to versions that address this specific memory handling issue. Additionally, applications should implement proper error handling around garbage collection calls and monitor for unexpected memory access violations. From a cybersecurity perspective, this vulnerability aligns with CWE-121 and CWE-122 categories related to buffer overflow conditions and memory corruption issues. The ATT&CK framework would classify this as a memory corruption technique that could potentially be leveraged in privilege escalation or denial of service attacks. Organizations should also implement runtime monitoring and intrusion detection systems to identify unusual garbage collection patterns that might indicate exploitation attempts, while maintaining regular security assessments to ensure all Lua-based applications are running patched versions.