CVE-2017-17816 in NASM
Summary
by MITRE
In Netwide Assembler (NASM) 2.14rc0, there is a use-after-free in pp_getline in asm/preproc.c that will cause a remote denial of service attack.
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-2017-17816 represents a critical use-after-free condition within the Netwide Assembler (NASM) version 2.14rc0, specifically within the preprocessor component. This flaw exists in the pp_getline function located in the asm/preproc.c source file, which is responsible for processing assembly code during the compilation phase. The issue arises when the assembler processes malformed or specially crafted input files that trigger improper memory management during preprocessing operations.
The technical implementation of this vulnerability stems from improper handling of memory allocation and deallocation within the preprocessor's input reading mechanism. When NASM encounters certain conditional assembly directives or macro expansions that lead to the pp_getline function being called multiple times with overlapping memory references, the system attempts to free memory that has already been deallocated or access memory that has been freed, creating a use-after-free scenario. This memory corruption condition occurs during the parsing of assembly source files that contain specific combinations of preprocessor directives, conditional compilation statements, and macro definitions.
The operational impact of this vulnerability manifests as a remote denial of service attack vector, where an attacker can craft malicious assembly source files that, when processed by NASM, will cause the assembler to crash or become unresponsive. The remote nature of this attack means that an attacker can exploit this vulnerability without requiring local access to the target system, making it particularly dangerous in environments where NASM is used to process untrusted input from external sources. This vulnerability can be exploited in automated build systems, online code compilation services, or any scenario where NASM processes assembly code from potentially malicious sources without proper input validation.
This vulnerability maps to CWE-416, which specifically addresses the use of memory after it has been freed, and represents a classic example of memory safety issues in C/C++ applications. The attack pattern aligns with the ATT&CK framework's technique T1203, which covers "Exploitation for Client Execution" through the exploitation of software vulnerabilities to cause system instability. The vulnerability demonstrates poor input validation practices and inadequate memory management within the preprocessor subsystem, making it a prime candidate for exploitation in automated attack scenarios.
The primary mitigation strategy involves upgrading to a patched version of NASM that addresses the memory management issues in the preprocessor component. System administrators should also implement input validation measures to filter or sanitize assembly source files before processing them with NASM. Additionally, organizations should consider implementing sandboxing mechanisms when processing untrusted assembly code to isolate the assembler from critical system resources and prevent potential exploitation of similar memory corruption vulnerabilities in other parts of the system.