CVE-2018-8881 in Netwide Assembler
Summary
by MITRE
Netwide Assembler (NASM) 2.13.02rc2 has a heap-based buffer over-read in the function tokenize in asm/preproc.c, related to an unterminated string.
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Analysis
by VulDB Data Team • 02/22/2023
The vulnerability identified as CVE-2018-8881 affects Netwide Assembler version 2.13.02rc2, a widely used x86 and x86-64 assembler for creating machine code from assembly language source files. This issue manifests as a heap-based buffer over-read within the tokenize function located in the asm/preproc.c source file, representing a critical memory safety flaw that can potentially lead to arbitrary code execution or system compromise. The vulnerability stems from improper handling of string termination within the preprocessing phase of assembly code compilation, where the assembler fails to properly null-terminate strings before processing them.
The technical implementation of this flaw occurs during the lexical analysis phase of NASM's preprocessing pipeline, where the tokenize function processes input assembly directives and operands without adequate bounds checking or string termination validation. When encountering certain malformed or specially crafted assembly input, the function reads beyond allocated memory boundaries, accessing heap memory that has not been properly initialized or terminated. This over-read condition creates a potential attack surface where malicious input can trigger memory corruption, leading to unpredictable program behavior including crashes, data corruption, or more severe exploitation vectors. The vulnerability specifically relates to CWE-125, which describes out-of-bounds read conditions, and CWE-787, which addresses out-of-bounds write conditions that can occur in similar contexts.
The operational impact of this vulnerability extends beyond simple compilation failures, as it can be exploited by attackers who craft malicious assembly code to trigger the buffer over-read condition. When NASM processes such malformed input, particularly in environments where assembly files are generated dynamically or sourced from untrusted inputs, the over-read can result in denial of service conditions or potentially enable remote code execution depending on the execution context. Attackers could leverage this vulnerability in scenarios where NASM is used in automated build systems, web-based assembly editors, or any environment where untrusted assembly code is processed. The vulnerability's exploitation potential aligns with ATT&CK technique T1059.001, which covers command and scripting interpreter usage, particularly when the assembler is part of larger build or compilation chains that could be manipulated through crafted assembly input.
Mitigation strategies for CVE-2018-8881 should prioritize immediate patching of affected NASM versions to the latest stable releases that contain fixes for the buffer over-read condition. System administrators and developers should implement input validation measures to sanitize assembly code inputs before processing them through NASM, particularly in environments where assembly files originate from external or untrusted sources. Additional protective measures include deploying memory protection mechanisms such as address space layout randomization and stack canaries to reduce exploitation success rates, along with implementing strict access controls on systems that execute NASM with elevated privileges. Organizations should also consider maintaining up-to-date vulnerability scanning tools that can detect the presence of vulnerable NASM versions in their environments, as well as establishing secure coding practices for assembly language processing that prevent similar buffer over-read conditions from occurring in other components of the build infrastructure.