CVE-2024-31852 in LLVM
Summary
by MITRE • 04/05/2024
LLVM before 18.1.3 generates code in which the LR register can be overwritten without data being saved to the stack, and thus there can sometimes be an exploitable error in the flow of control. This affects the ARM backend and can be demonstrated with Clang. NOTE: the vendor perspective is "we don't have strong objections for a CVE to be created ... It does seem that the likelihood of this miscompile enabling an exploit remains very low, because the miscompile resulting in this JOP gadget is such that the function is most likely to crash on most valid inputs to the function. So, if this function is covered by any testing, the miscompile is most likely to be discovered before the binary is shipped to production."
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Analysis
by VulDB Data Team • 02/11/2025
The vulnerability identified as CVE-2024-31852 represents a significant code generation flaw within the LLVM compiler infrastructure affecting versions prior to 18.1.3. This issue specifically targets the ARM backend implementation and manifests through improper handling of the Link Register (LR) during code generation processes. The problem occurs when the compiler generates machine code where the LR register gets overwritten without ensuring that the original value is properly saved to the stack, creating a potential path for control flow manipulation. The vulnerability is particularly concerning because it can lead to unintended program behavior that may be exploited in certain circumstances, though the vendor has noted that exploitation likelihood remains quite low due to the inherent instability of the generated code.
The technical nature of this flaw stems from the compiler's failure to properly manage register state during function prologue and epilogue generation on ARM architectures. When LLVM processes ARM backend code, it occasionally fails to correctly preserve the LR register value before overwriting it with new data. This creates a situation where the return address information stored in the LR register becomes corrupted or lost, potentially leading to unpredictable program execution paths. The issue is classified under CWE-676 as the use of potentially dangerous functions and can be categorized under ATT&CK technique T1059.007 for process injection and T1070.006 for indicator removal through manipulation of stack frames. The miscompilation results in what security researchers refer to as a Jump-Oriented Programming (JOP) gadget, where the corrupted control flow can be leveraged to redirect program execution.
The operational impact of this vulnerability extends beyond simple compiler correctness issues, as it creates potential security risks in environments where ARM-based systems execute compiled code. The vulnerability affects Clang compiler users targeting ARM architectures, particularly in embedded systems, mobile devices, and IoT applications where ARM processors dominate. While the vendor assessment suggests that the miscompile is likely to cause crashes during normal execution rather than enabling stable exploitation, the nature of compiler bugs means that undetected miscompilations could persist in production environments. The risk is further compounded by the fact that such issues may not be immediately apparent during development testing phases, especially when functions are not thoroughly tested with edge cases or when automated testing suites fail to cover the specific code paths that trigger the miscompilation.
Mitigation strategies for CVE-2024-31852 primarily involve upgrading to LLVM version 18.1.3 or later where the code generation logic has been corrected to properly handle the LR register preservation. Organizations should prioritize patching their compiler toolchains, particularly in development environments where ARM-based compilation occurs. Additional mitigations include implementing comprehensive testing procedures that specifically target ARM backend code generation, utilizing static analysis tools that can detect potential register preservation issues, and conducting thorough regression testing of compiled code on ARM platforms. Security teams should also consider monitoring for unusual crash patterns or unexpected behavior in ARM-based applications that might indicate the presence of this miscompilation. The vulnerability demonstrates the critical importance of compiler correctness in security-sensitive environments and underscores the need for continuous verification of compiler outputs, especially in architectures where register management is complex and error-prone. Organizations should also consider implementing runtime protections such as stack canaries or control flow integrity mechanisms to provide additional defense in depth against potential exploitation attempts that might arise from such compiler miscompilations.