CVE-2018-19209 in Netwide Assembler
Summary
by MITRE
Netwide Assembler (NASM) 2.14rc15 has a NULL pointer dereference in the function find_label in asm/labels.c that will lead to a DoS attack.
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Analysis
by VulDB Data Team • 04/11/2020
The vulnerability identified as CVE-2018-19209 represents a critical null pointer dereference flaw within the Netwide Assembler version 2.14rc15, specifically within the find_label function located in the asm/labels.c source file. This issue manifests when the assembler processes malformed input containing certain label references that trigger the function to attempt accessing a null pointer, resulting in an immediate program termination or denial of service condition. The vulnerability affects the core functionality of the assembler, which is widely used in software development and system programming contexts for translating assembly language source code into machine code. The flaw occurs during the label resolution phase of assembly processing, where the assembler maintains internal data structures to track symbol references and their corresponding memory locations. When encountering specific malformed input patterns, the find_label function fails to properly validate pointer references before dereferencing them, creating an exploitable condition that can be leveraged by attackers to disrupt normal assembler operations.
The technical implementation of this vulnerability stems from inadequate input validation within the label handling subsystem of NASM. The find_label function is responsible for locating previously defined labels within the assembler's symbol table, but it fails to check whether the internal data structures it references contain valid pointers before attempting to access them. This type of error falls under the Common Weakness Enumeration category CWE-476, which specifically addresses NULL pointer dereference conditions in software implementations. The vulnerability is particularly concerning because it represents a classic denial of service attack vector that can be triggered through controlled input manipulation without requiring complex exploitation techniques or elevated privileges. The flaw exists in the software's defensive programming practices where proper null checks are missing from critical code paths, allowing execution to proceed into invalid memory access scenarios.
The operational impact of CVE-2018-19209 extends beyond simple program termination, as it can severely disrupt development workflows and automated build processes that rely on NASM for assembly code compilation. In continuous integration environments, this vulnerability can cause build failures and pipeline interruptions, potentially blocking software releases or updates. The vulnerability affects developers, system administrators, and automated toolchains that depend on NASM's reliable operation for generating executable code. When exploited, the null pointer dereference causes the assembler to crash immediately, which can be particularly problematic in large-scale development environments where multiple assembly files are processed simultaneously. The DoS condition affects not just individual assembly operations but can cascade into broader system reliability issues when the assembler is part of larger compilation toolchains or when multiple instances of the vulnerability are triggered in sequence.
Mitigation strategies for CVE-2018-19209 should focus on immediate patching of the affected NASM version to address the null pointer dereference issue through proper input validation and pointer checking mechanisms. Organizations should prioritize updating to the latest stable release of NASM that includes the fix for this vulnerability, as the patch typically involves adding null checks before pointer dereferencing operations within the find_label function. Additionally, defensive programming practices should be implemented to ensure that all pointer accesses are validated before use, following the principle of least privilege and input sanitization. Security monitoring should include detection of unusual assembler behavior or crash patterns that might indicate exploitation attempts. The vulnerability also highlights the importance of robust software testing practices including fuzzing and boundary condition testing to identify similar null pointer dereference conditions in other components of the software ecosystem. Organizations should consider implementing input validation layers or sandboxing mechanisms when processing untrusted assembly code to prevent exploitation of similar vulnerabilities in other tools within their development infrastructure.