CVE-2019-14871 in newlib
Summary
by MITRE
The REENT_CHECK macro (see newlib/libc/include/sys/reent.h) as used by REENT_CHECK_TM, REENT_CHECK_MISC, REENT_CHECK_MP and other newlib macros in verisons prior to 3.3.0, does not check for memory allocation problems when the DEBUG flag is unset (as is the case in production firmware builds).
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Analysis
by VulDB Data Team • 04/17/2024
The vulnerability identified as CVE-2019-14871 resides within the newlib C library implementation, specifically affecting versions prior to 3.3.0. This issue manifests through the REENT_CHECK macro family which includes REENT_CHECK_TM, REENT_CHECK_MISC, REENT_CHECK_MP and related macros. These macros are designed to provide debugging capabilities for reentrancy checking in embedded systems and firmware environments where memory management is critical. The fundamental flaw lies in the conditional compilation logic that governs when these checks are performed, creating a dangerous disparity between development and production environments.
The technical implementation of this vulnerability stems from the fact that REENT_CHECK macros rely on DEBUG flag compilation directives to determine whether memory allocation validation should occur. When the DEBUG flag is enabled during compilation, these macros perform proper memory allocation checks to ensure that reentrant resources are properly managed. However, in production firmware builds where DEBUG is typically unset for performance and size optimization reasons, these crucial checks are entirely omitted. This creates a scenario where memory allocation failures can occur silently without any validation, potentially leading to memory corruption, system instability, or exploitable conditions in embedded environments.
The operational impact of this vulnerability extends significantly in embedded systems and firmware contexts where newlib is commonly deployed. Firmware developers often build production images without DEBUG flags to reduce code size and improve execution performance, inadvertently exposing their systems to memory management issues that could be exploited by attackers. The vulnerability creates a false sense of security where applications appear to function normally but may be silently corrupting memory structures. This is particularly concerning in IoT devices, medical equipment, automotive systems, and industrial control systems where firmware reliability is paramount. The absence of allocation validation means that even minor memory allocation failures can cascade into system-wide failures or create exploitable memory corruption conditions.
The vulnerability aligns with CWE-664, which addresses improper control of a resource through lifetime management, and CWE-704, which covers incorrect type conversion or cast. From an ATT&CK perspective, this weakness maps to T1059.001 for command and script injection, T1203 for Exploitation for Client Execution, and T1499.001 for Network Denial of Service. The lack of proper memory allocation validation creates opportunities for attackers to manipulate memory layout through carefully crafted inputs that trigger allocation failures, potentially leading to privilege escalation or system compromise. Organizations should immediately upgrade to newlib version 3.3.0 or later where proper memory allocation checks are implemented regardless of DEBUG flag status. Additionally, system architects should implement comprehensive memory monitoring and validation in firmware environments, and consider static analysis tools that can detect similar patterns in custom code implementations.