CVE-2018-19216 in Netwide Assembler
Summary
by MITRE
Netwide Assembler (NASM) before 2.13.02 has a use-after-free in detoken at asm/preproc.c.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 06/05/2023
The vulnerability identified as CVE-2018-19216 represents a critical use-after-free condition within the Netwide Assembler (NASM) tool, specifically affecting versions prior to 2.13.02. This flaw exists in the detoken function located within the asm/preproc.c source file, making it a significant security concern for developers and system administrators who rely on NASM for assembly code compilation. The issue stems from improper memory management during the preprocessing phase of assembly code processing, where freed memory locations are accessed after being deallocated, creating potential vectors for arbitrary code execution or system instability.
The technical implementation of this vulnerability involves the detoken function's failure to properly manage memory references during the parsing of assembly directives and tokens. When NASM processes certain input files containing maliciously crafted assembly constructs, the preprocessor module executes the detoken function which handles tokenization of assembly language elements. The flaw manifests when the function deallocates memory associated with token structures but continues to reference these freed locations, leading to undefined behavior. This memory corruption can be exploited by attackers who craft specific assembly input files that trigger the vulnerable code path, potentially allowing for remote code execution or privilege escalation depending on the execution context.
From an operational impact perspective, this vulnerability affects any system utilizing NASM versions before 2.13.02 for compiling assembly code, including development environments, build servers, and automated compilation systems. The exploitability of this flaw is heightened in scenarios where NASM processes untrusted assembly input from external sources or user-provided code, making it particularly dangerous in web applications or build systems that accept user-generated assembly code. The vulnerability aligns with CWE-416, which specifically addresses use-after-free errors in memory management, and demonstrates characteristics consistent with ATT&CK technique T1059.008 for the execution of malicious code through assembly language manipulation. Systems that automatically compile assembly code without proper input validation become prime targets for exploitation, as the vulnerability can be triggered through legitimate compilation workflows.
The recommended mitigation strategy centers on immediate upgrade to NASM version 2.13.02 or later, which includes patches addressing the memory management issues in the detoken function. Organizations should also implement strict input validation measures for any assembly code processing workflows, particularly when handling untrusted inputs. Additional protective measures include running NASM in restricted environments with limited privileges, employing sandboxing techniques for assembly compilation processes, and implementing automated code scanning for potentially malicious assembly constructs. Security teams should monitor their systems for any instances where NASM is used in automated build processes or with user-provided content, ensuring that all instances are updated to patched versions. The vulnerability serves as a reminder of the importance of memory safety in compiler toolchains and the critical need for regular security updates in development tools that handle code compilation and processing.