CVE-2019-14877: 
NixOS vulnerability analysis and mitigation

In the __mdiff function of the newlib libc library, all versions prior to 3.3.0 (see newlib/libc/stdlib/mprec.c), Balloc is used to allocate big integers, however no check is performed to verify if the allocation succeeded or not. The access to _wds and _sign will trigger a null pointer dereference bug in case of a memory allocation failure (CENSUS Advisory, NVD).

The vulnerability is a NULL pointer dereference issue (CWE-476) that occurs in the __mdiff function when allocating big integers using Balloc without proper allocation failure checks. When memory allocation fails, subsequent accesses to _wds and _sign members will trigger null pointer dereference bugs. The vulnerability has a CVSS v3.1 Base Score of 6.5 MEDIUM (Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) (NVD).

A successful exploitation of this vulnerability can result in a null pointer dereference, potentially leading to a program crash or denial of service condition. On embedded systems where the Device Vector Table is mapped at address 0x0, reading or writing through the null pointer could potentially leak interrupt handler addresses or overwrite interrupt handlers (CENSUS Advisory).

Users are strongly advised to update to newlib version 3.3.0 or later, which includes patches for this vulnerability. Library authors are recommended to always check for NULL return values from memory allocators and either pass the NULL value up to the caller or execute a predefined 'out of memory' handler (CENSUS Advisory).