CVE-2017-17820 in Netwide Assembler
Summary
by MITRE
In Netwide Assembler (NASM) 2.14rc0, there is a use-after-free in pp_list_one_macro in asm/preproc.c that will lead to a remote denial of service attack, related to mishandling of operand-type errors.
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Analysis
by VulDB Data Team • 05/31/2020
The vulnerability identified as CVE-2017-17820 resides within the Netwide Assembler (NASM) version 2.14rc0, a widely used assembler for x86 and x86-64 architectures. This flaw manifests as a use-after-free condition in the pp_list_one_macro function located within the asm/preproc.c source file, representing a critical memory safety issue that can be exploited remotely. The vulnerability specifically occurs during the preprocessing phase of assembly code compilation when handling operand-type errors, creating a scenario where freed memory locations are accessed after being deallocated, potentially leading to unpredictable behavior.
The technical exploitation of this vulnerability involves manipulating assembly source code containing malformed operand specifications that trigger the problematic code path. When NASM processes such inputs, the preprocessor attempts to handle operand-type errors through the pp_list_one_macro function, which fails to properly manage memory allocation and deallocation sequences. This improper memory handling creates a use-after-free condition where pointers referencing freed memory regions are subsequently accessed, leading to potential crashes or system instability. The vulnerability's remote exploitability stems from NASM's capability to process external input files, making it susceptible to malicious code injection through crafted assembly source files.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a fundamental memory corruption issue that could potentially be leveraged for more sophisticated attacks. Attackers could craft malicious assembly files that, when processed by vulnerable NASM versions, would cause the assembler to crash or behave unpredictably, effectively denying service to legitimate users. The vulnerability affects systems where NASM is used for automated build processes, continuous integration pipelines, or any environment where assembly code is compiled from untrusted sources. Given the widespread use of NASM in software development and system programming, this vulnerability presents a significant risk to development environments and build servers.
Mitigation strategies for CVE-2017-17820 should prioritize immediate patching of affected NASM installations to version 2.14 or later, which contains the necessary memory management fixes. Organizations should implement input validation measures for assembly source files, particularly in automated build environments where untrusted code might be processed. Security-conscious developers should also consider implementing sandboxing mechanisms when processing assembly code from external sources, limiting the potential impact of exploitation. The vulnerability aligns with CWE-416, which describes the use-after-free error condition, and could potentially map to ATT&CK technique T1059.001 for execution through command-line interfaces when exploited in build environments. System administrators should monitor for any unusual process behavior or crashes in systems where NASM is actively used, as these could indicate exploitation attempts.