CVE-2018-19215 in Netwide Assembler
Summary
by MITRE
Netwide Assembler (NASM) 2.14rc16 has a heap-based buffer over-read in expand_mmac_params in asm/preproc.c for the special cases of the % and $ and ! characters.
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Analysis
by VulDB Data Team • 06/05/2023
The vulnerability CVE-2018-19215 represents a critical heap-based buffer over-read flaw in the Netwide Assembler (NASM) version 2.14rc16, specifically within the expand_mmac_params function located in the asm/preproc.c source file. This issue manifests when processing special character sequences involving the %, $, and ! symbols, which are commonly used in macro definitions and preprocessing operations within assembly language source code. The vulnerability stems from insufficient bounds checking during the expansion of macro parameters, allowing an attacker to potentially read memory beyond the allocated buffer boundaries.
The technical implementation of this flaw occurs during the preprocessing phase of NASM when handling macro expansions that contain the affected special characters. When the assembler encounters these specific character combinations, the expand_mmac_params function fails to properly validate the length of data being processed, leading to a situation where memory reads extend beyond the intended buffer limits. This over-read condition can result in the disclosure of sensitive information from adjacent memory locations, potentially including stack contents, heap data, or other program state information that may be accessible to an attacker. The vulnerability is classified as a heap-based buffer over-read, which is a variant of the more general buffer overflow category but specifically affects heap-allocated memory regions rather than stack memory.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can enable more sophisticated attack vectors including potential code execution or system compromise. An attacker who can control the input to NASM during preprocessing could craft malicious assembly source files containing the specific character sequences that trigger the over-read condition. This scenario becomes particularly concerning in environments where NASM is used to process untrusted input, such as in automated build systems, code analysis tools, or compiler infrastructure. The vulnerability affects the core preprocessing functionality of NASM, making it a critical issue for any system that relies on this assembler for processing assembly code. According to CWE classification, this represents a CWE-125: Out-of-bounds Read vulnerability, which is a well-documented weakness in software security practices and is often exploited in various attack scenarios including information leakage and privilege escalation attempts.
Mitigation strategies for CVE-2018-19215 should focus on immediate patching of the affected NASM version to the latest stable release that contains the fix for this buffer over-read condition. Organizations should also implement input validation measures to prevent untrusted assembly code from being processed through their NASM-based tools, particularly in automated environments. Additionally, deployment of runtime protections such as address space layout randomization and stack canaries can help mitigate potential exploitation attempts. The vulnerability aligns with ATT&CK technique T1059.006 for executing malicious code through macro processing, and T1550.001 for privilege escalation through compiler toolchain exploitation. System administrators should also consider implementing network segmentation and access controls to limit exposure of systems that process assembly code, particularly in environments where NASM is used for automated code generation or compilation processes. Regular security assessments of build environments and code analysis tools should include verification that all components are running patched versions to prevent exploitation of known vulnerabilities in the assembler toolchain.