CVE-2020-24369 in Lua
Summary
by MITRE
ldebug.c in Lua 5.4.0 attempts to access debug information via the line hook of a stripped function, leading to a NULL pointer dereference.
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Analysis
by VulDB Data Team • 08/18/2020
The vulnerability identified as CVE-2020-24369 resides within the Lua 5.4.0 interpreter's debugging subsystem, specifically in the ldebug.c source file. This issue manifests when the debugger attempts to access debug information through the line hook mechanism while processing a stripped function. Stripped functions lack debugging metadata and symbol information, creating a scenario where the debugging infrastructure encounters a NULL pointer during normal operation. The root cause stems from inadequate null pointer validation within the debug information retrieval process, particularly when the line hook mechanism is invoked on functions that have been processed to remove debugging symbols.
The technical flaw represents a classic null pointer dereference vulnerability that occurs in the context of dynamic debugging operations. When Lua's debugging infrastructure encounters a stripped function, the internal data structures that normally contain debug information become null or invalid, yet the line hook mechanism does not properly validate these pointers before attempting to access them. This behavior directly aligns with CWE-476 which categorizes NULL pointer dereference as a fundamental programming error that can lead to application crashes or potentially exploitable conditions. The vulnerability is particularly concerning because it can be triggered during normal program execution when debugging features are enabled, making it a reliable crash vector that affects the interpreter's stability.
The operational impact of this vulnerability extends beyond simple application crashes to potentially disrupting debugging workflows and system stability. When a Lua application encounters a stripped function during debugging, the interpreter will crash with a segmentation fault or similar memory access violation, effectively terminating the debugging session. This can significantly hamper development and troubleshooting processes, particularly in environments where Lua is used for embedded systems or applications requiring robust debugging capabilities. The vulnerability affects all versions of Lua 5.4.0 and potentially impacts any application that relies on the interpreter's debugging features while processing code that has been stripped of debug symbols.
Mitigation strategies for CVE-2020-24369 should focus on both immediate code-level fixes and operational best practices. The primary fix involves implementing proper null pointer validation within the ldebug.c file before accessing debug information structures, ensuring that the line hook mechanism gracefully handles stripped functions without attempting to dereference NULL pointers. Organizations should also consider updating to patched versions of Lua 5.4.0 or later releases that address this specific vulnerability. From a defensive perspective, system administrators should monitor for applications using Lua with debugging enabled and ensure proper input validation when processing external code. The vulnerability demonstrates the importance of robust error handling in debugging subsystems and aligns with ATT&CK technique T1059.007 for Lua scripting, highlighting the need for secure coding practices in interpreted languages. Additionally, this issue underscores the broader challenge of maintaining security in debugging infrastructure, where seemingly benign operations can expose critical system vulnerabilities through improper pointer validation.