CVE-2019-7147 in Netwide Assembler
Summary
by MITRE
A buffer over-read exists in the function crc64ib in crc64.c in nasmlib in Netwide Assembler (NASM) 2.14rc16. A crafted asm input can cause segmentation faults, leading to denial-of-service.
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Analysis
by VulDB Data Team • 05/06/2020
The vulnerability identified as CVE-2019-7147 represents a critical buffer over-read condition within the Netwide Assembler (NASM) version 2.14rc16, specifically within the nasmlib library's crc64ib function located in crc64.c. This flaw manifests when processing specially crafted assembly input files that trigger an improper bounds check during cyclic redundancy check calculation operations. The issue stems from insufficient validation of input data lengths against the allocated buffer space, creating a scenario where the function attempts to read memory beyond the intended buffer boundaries. Such behavior fundamentally violates memory safety principles and creates exploitable conditions that can be leveraged by malicious actors to disrupt normal system operations.
The technical implementation of this vulnerability resides in the crc64ib function which handles CRC64 calculations for assembly code processing. When NASM encounters specific input patterns designed to trigger this condition, the function fails to properly validate the length of incoming data against the predetermined buffer limits. This oversight creates a classic buffer over-read scenario where the program attempts to access memory locations that extend beyond the allocated buffer space. The vulnerability is categorized under CWE-125 as an "Out-of-bounds Read" which directly aligns with the observed behavior of accessing memory beyond valid buffer boundaries. The flaw specifically affects the nasmlib component of NASM, which serves as the core library for assembling source code into executable machine instructions, making it a critical component in the assembly pipeline.
The operational impact of CVE-2019-7147 extends beyond simple denial-of-service conditions to potentially compromise system stability and availability. When exploited, the buffer over-read causes segmentation faults that result in immediate program termination, effectively preventing legitimate assembly operations from completing successfully. This denial-of-service vulnerability can be particularly damaging in automated build environments or continuous integration systems where NASM is used as part of the compilation pipeline. Attackers can leverage this flaw by crafting malicious assembly files that, when processed by NASM, trigger the segmentation fault and cause system crashes or hangs. The vulnerability's impact is amplified in environments where NASM is used frequently or in automated workflows, as a single malicious input can disrupt multiple processes or services that depend on successful assembly operations.
Mitigation strategies for CVE-2019-7147 should prioritize immediate patching of NASM installations to versions that address the buffer over-read condition in the crc64ib function. System administrators should implement input validation measures to filter potentially malicious assembly code before processing, particularly in environments where untrusted inputs are processed. The vulnerability's classification under the ATT&CK framework would align with techniques involving process injection and privilege escalation through software exploitation, though the immediate impact is limited to denial-of-service. Organizations should also consider implementing sandboxing mechanisms for assembly processing to contain potential impacts, while monitoring for unusual assembly behavior that might indicate exploitation attempts. Additionally, security teams should review their build processes to ensure that only trusted assembly code is processed through NASM, and implement proper error handling and logging to detect potential exploitation attempts. The fix typically involves adding proper bounds checking to validate input lengths against allocated buffer sizes, ensuring that all memory access operations remain within legitimate boundaries as recommended by secure coding practices and industry standards for preventing buffer overflow conditions.