CVE-2020-24370 in Lua
Summary
by MITRE • 01/25/2023
ldebug.c in Lua 5.4.0 allows a negation overflow and segmentation fault in getlocal and setlocal, as demonstrated by getlocal(3,2^31).
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Analysis
by VulDB Data Team • 12/12/2024
The vulnerability identified as CVE-2020-24370 resides within the Lua 5.4.0 interpreter's debugging functionality, specifically in the ldebug.c source file. This issue manifests as a negation overflow condition that leads to a segmentation fault when executing certain debugging operations. The flaw occurs during the processing of local variable access operations through the getlocal and setlocal functions, which are integral components of Lua's debugging API. The vulnerability is particularly concerning because it can be triggered through a simple debugging command sequence that leverages an integer overflow condition.
The technical exploitation of this vulnerability involves passing a specific parameter value to the getlocal function where the second argument equals 2^31, which represents the maximum value for a 32-bit signed integer. When this value is processed within the debugging subsystem, the negation operation fails to properly handle the overflow condition, resulting in a memory access violation that manifests as a segmentation fault. This behavior stems from improper bounds checking within the debugging implementation where negative values are not adequately validated before being used in array indexing operations or memory access calculations. The underlying cause can be categorized under CWE-191, which describes integer underflow or wraparound conditions, and more specifically relates to CWE-128, which addresses negative integer underflow.
The operational impact of this vulnerability extends beyond simple crash conditions as it represents a potential denial of service vector that could be exploited by malicious actors to disrupt applications relying on Lua's debugging capabilities. In environments where Lua is embedded within larger applications or systems, this vulnerability could allow attackers to cause application instability or complete system crashes, potentially leading to service disruption. The vulnerability is particularly dangerous in server-side applications or embedded systems where continuous operation is critical, as it could enable attackers to repeatedly trigger the segmentation fault and maintain persistent service disruption. Additionally, since this affects the debugging functionality, it could potentially be used as part of a broader exploitation chain where an attacker might attempt to bypass other security mechanisms by causing system instability.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected Lua installations to version 5.4.1 or later, which contains the necessary fixes for the integer overflow condition in the debugging subsystem. Organizations should also implement runtime monitoring to detect anomalous debugging API usage patterns that might indicate exploitation attempts. The fix typically involves proper bounds checking and overflow validation within the getlocal and setlocal function implementations, ensuring that parameter values are validated before being used in memory operations. Security teams should consider implementing application whitelisting or sandboxing measures for Lua environments, particularly in production systems where debugging functionality is not required. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving denial of service through resource exhaustion or system instability, and could potentially be used as a precursor to more sophisticated attacks if the system allows for arbitrary code execution following the initial crash condition.