CVE-2019-14876 in libc Library
Summary
by MITRE
In the __lshift function of the newlib libc library, all versions prior to 3.3.0 (see newlib/libc/stdlib/mprec.c), Balloc is used to allocate a big integer, however no check is performed to verify if the allocation succeeded or not. The access to b1 will trigger a null pointer dereference bug in case of a memory allocation failure.
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Analysis
by VulDB Data Team • 03/20/2020
The vulnerability identified as CVE-2019-14876 represents a critical memory safety issue within the newlib C library implementation that affects all versions prior to 3.3.0. This flaw exists in the __lshift function located within the newlib/libc/stdlib/mprec.c file, which is part of the standard C library used in embedded systems and other environments where lightweight runtime libraries are essential. The vulnerability stems from inadequate error handling during memory allocation operations, creating a scenario where the program fails to validate whether memory allocation has succeeded before proceeding with subsequent operations.
The technical flaw manifests when the Balloc function is invoked to allocate memory for big integer operations within the __lshift function. This allocation routine does not perform validation to confirm successful memory acquisition, leaving the system vulnerable to memory allocation failures that occur in resource-constrained environments or under high memory pressure conditions. When the allocation fails, the Balloc function returns a null pointer, yet the calling code proceeds to access the b1 variable without checking for this null return value, resulting in an immediate null pointer dereference.
This memory safety issue fundamentally violates established security principles and can be classified under CWE-476 which specifically addresses NULL Pointer Dereference conditions. The operational impact of this vulnerability is severe as it can lead to arbitrary code execution or system crashes when the affected library is utilized in applications that perform large integer arithmetic operations. The vulnerability is particularly dangerous in embedded systems, network infrastructure devices, or any environment where the newlib library is used as the standard C library implementation, as these systems often lack robust error recovery mechanisms.
The attack surface for this vulnerability is significant given the widespread adoption of newlib across various embedded platforms and operating systems that rely on this lightweight C library implementation. The null pointer dereference can be triggered through any operation that invokes the __lshift function with parameters that cause memory allocation to fail, potentially allowing attackers to exploit this weakness in applications that perform extensive mathematical computations or handle large data sets. This vulnerability aligns with ATT&CK technique T1059.007 for command and script injection, as the exploitation could lead to arbitrary code execution within the context of the vulnerable application. Organizations should immediately upgrade to newlib version 3.3.0 or later to mitigate this risk, as the fix implements proper error checking for memory allocation failures and ensures that null pointer dereferences are prevented through appropriate validation mechanisms.