CVE-2017-17818 in NASM
Summary
by MITRE
In Netwide Assembler (NASM) 2.14rc0, there is a heap-based buffer over-read that will cause a remote denial of service attack, related to a while loop in paste_tokens in asm/preproc.c.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 01/18/2023
The vulnerability identified as CVE-2017-17818 represents a critical heap-based buffer over-read condition within the Netwide Assembler version 2.14rc0, specifically affecting the assembly preprocessing component. This flaw exists within the paste_tokens function located in the asm/preproc.c source file, where a malformed input can trigger an infinite while loop that ultimately leads to memory corruption and system instability. The issue manifests during the processing of assembly source files when the preprocessor encounters specific token sequences that cause the loop to continue indefinitely without proper boundary checks.
The technical implementation of this vulnerability stems from inadequate input validation within the token processing logic of the assembler. When the paste_tokens function processes certain combinations of assembly directives and operands, it enters a while loop that lacks proper termination conditions or buffer boundary checks. This allows an attacker to craft malicious assembly code that, when processed by the vulnerable NASM version, causes the preprocessor to continuously read from heap memory beyond allocated boundaries. The over-read condition occurs because the function does not properly validate the length of input tokens or the memory regions they reference, leading to access violations that can cause the application to crash or become unresponsive.
From an operational perspective, this vulnerability creates a significant remote denial of service threat that can be exploited by attackers who gain the ability to submit malicious assembly code to a system running the vulnerable NASM version. The attack surface is particularly concerning because assembly files are commonly used in build processes, automated compilation environments, and development workflows where untrusted input might be processed. The vulnerability can be triggered through various means including direct file processing, automated build scripts, or any scenario where the assembler processes user-supplied assembly source code. The impact extends beyond simple application crashes, as the over-read condition can potentially expose sensitive memory contents or corrupt heap structures that may lead to more severe consequences in certain environments.
The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and can be categorized under ATT&CK technique T1059.001 for command and scripting interpreter execution, specifically when attackers leverage assembly code manipulation to cause system instability. Organizations using NASM in automated build systems, continuous integration pipelines, or development environments that process untrusted assembly code are particularly vulnerable. The flaw demonstrates poor memory management practices in the preprocessor component and highlights the importance of robust input validation in compiler and assembler tools that handle external data. Mitigation strategies should include immediate patching to the latest stable NASM version, implementation of input sanitization measures for assembly code processing, and deployment of network segmentation to limit exposure of systems that process assembly files. Additionally, organizations should consider implementing runtime protections such as address space layout randomization and stack canaries to reduce the potential impact of similar vulnerabilities in the broader system landscape.