CVE-2018-8882 in Netwide Assembler
Summary
by MITRE
Netwide Assembler (NASM) 2.13.02rc2 has a stack-based buffer under-read in the function ieee_shr in asm/float.c via a large shift value.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 01/15/2020
The vulnerability identified as CVE-2018-8882 resides within the Netwide Assembler (NASM) version 2.13.02rc2, a widely used assembler for the x86 architecture that translates assembly language source code into machine code. This particular flaw manifests as a stack-based buffer under-read within the ieee_shr function located in the asm/float.c source file, representing a critical security weakness that can potentially be exploited by malicious actors. The issue specifically occurs when processing assembly code containing floating-point operations with excessively large shift values, creating a scenario where the program attempts to read memory locations that lie below the allocated buffer boundaries on the stack.
The technical nature of this vulnerability stems from inadequate input validation within the ieee_shr function, which handles floating-point shift operations during the assembly process. When a user provides a large shift value that exceeds the expected range, the function fails to properly bounds-check the input parameter before using it to calculate memory offsets. This deficiency creates a condition where the program accesses memory locations that are not part of the intended buffer, potentially reading uninitialized stack data or data from adjacent memory regions. The under-read behavior occurs because the calculation used to determine the memory access offset results in a negative value that points to memory locations below the buffer's starting address, violating fundamental memory safety principles.
The operational impact of CVE-2018-8882 extends beyond simple program instability, as this vulnerability can potentially lead to information disclosure, denial of service, or even remote code execution depending on the specific environment and exploitation context. Attackers could leverage this weakness by crafting malicious assembly source files containing oversized shift values that trigger the under-read condition during the assembly process. The vulnerability affects any system running NASM 2.13.02rc2 when processing untrusted assembly code, making it particularly dangerous in environments where assembly files are generated or processed from external sources. The stack-based nature of the under-read means that the vulnerability could expose sensitive information from the program's stack memory, potentially including cryptographic keys, passwords, or other confidential data that may have been stored in adjacent memory locations.
Mitigation strategies for this vulnerability should prioritize immediate patching of NASM to versions that have addressed the buffer under-read issue through proper input validation and bounds checking mechanisms. System administrators should implement strict input validation for all assembly code processing pipelines, particularly when dealing with untrusted inputs from external sources. The fix typically involves adding proper range checks to ensure that shift values remain within acceptable limits before they are used in memory calculations, preventing the under-read condition from occurring. Additionally, organizations should consider implementing sandboxing mechanisms when processing assembly code to limit the potential impact of any remaining vulnerabilities. This vulnerability aligns with CWE-129, which describes improper validation of array indices, and may map to ATT&CK technique T1059.008 for execution through assembly languages, emphasizing the importance of secure coding practices in assembler development and the potential for exploitation through malicious code injection attacks.
The broader implications of this vulnerability highlight the critical importance of memory safety in low-level programming tools, particularly those used in security-sensitive environments where assembly language processing is common. Assemblers like NASM form the foundation of many security-critical applications and systems, making vulnerabilities within their codebases particularly concerning. The vulnerability demonstrates how seemingly minor input validation oversights in mathematical operations can lead to significant security implications, reinforcing the need for comprehensive security testing and code review practices in development toolchains. Organizations should maintain updated inventories of all assembly processing tools and ensure regular security updates are applied to prevent exploitation of known vulnerabilities that could compromise system integrity.