CVE-2019-8343 in Netwide Assembler
Summary
by MITRE
In Netwide Assembler (NASM) 2.14.02, there is a use-after-free in paste_tokens in asm/preproc.c.
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Analysis
by VulDB Data Team • 07/10/2023
The vulnerability identified as CVE-2019-8343 resides within the Netwide Assembler (NASM) version 2.14.02, a widely used x86 and x86-64 assembler for creating machine code from assembly language source files. This particular flaw manifests as a use-after-free condition in the paste_tokens function located within the asm/preproc.c source file, representing a critical memory safety issue that can potentially be exploited by malicious actors. The vulnerability occurs during the preprocessing phase of assembly code compilation, where the assembler handles token concatenation operations that are fundamental to macro processing and conditional assembly directives.
The technical implementation of this use-after-free vulnerability stems from improper memory management within the paste_tokens function which is responsible for combining multiple tokens into single entities during preprocessing. When the assembler processes certain complex macro expansions or conditional assembly constructs, it may attempt to access memory locations that have already been freed or reallocated, creating a scenario where subsequent operations can read from or write to deallocated memory regions. This flaw specifically arises from the lack of proper reference counting or memory lifecycle management when handling token concatenation operations, particularly when dealing with nested macros or complex preprocessing directives that involve token merging.
The operational impact of CVE-2019-8343 extends beyond simple program crashes, as this use-after-free condition creates potential attack vectors for remote code execution or denial-of-service scenarios. An attacker who can craft malicious assembly source code containing specific macro constructs could potentially trigger the vulnerability during compilation, leading to unpredictable program behavior including crashes, data corruption, or in more severe cases, arbitrary code execution if the memory corruption affects critical program structures. The vulnerability affects any system running NASM 2.14.02 where assembly source files containing specially crafted macros are processed, making it particularly concerning for automated build systems or development environments that compile user-provided assembly code without proper sanitization.
From a cybersecurity perspective, this vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software implementations. The flaw demonstrates poor memory management practices that violate fundamental security principles, as it allows for memory access patterns that can be manipulated to achieve unauthorized code execution. The ATT&CK framework categorizes this type of vulnerability under software exploitation techniques, specifically targeting memory corruption vulnerabilities that enable privilege escalation and system compromise. Organizations utilizing NASM for assembly code compilation should consider this vulnerability as a potential entry point for attackers seeking to compromise development environments or build servers that process untrusted assembly source code.
Mitigation strategies for CVE-2019-8343 primarily involve upgrading to a patched version of NASM where the memory management issues in paste_tokens have been resolved through proper memory lifecycle handling and validation of token operations. System administrators should implement strict input validation for assembly source files, particularly in automated build environments where untrusted code execution is possible. Additionally, deploying runtime protections such as address space layout randomization and stack canaries can provide defense-in-depth measures against potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of memory safety in compiler and assembler implementations, where seemingly minor flaws in preprocessing logic can create significant security risks for entire development ecosystems.