CVE-2021-45257 in NASM
Summary
by MITRE • 12/22/2021
An infinite loop vulnerability exists in nasm 2.16rc0 via the gpaste_tokens function.
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Analysis
by VulDB Data Team • 12/25/2021
The vulnerability identified as CVE-2021-45257 represents a critical infinite loop condition within the nasm assembler version 2.16rc0, specifically within the gpaste_tokens function. This flaw manifests as a denial of service vulnerability that can be exploited through crafted input sequences, potentially causing the assembler to enter an endless loop during processing operations. The issue stems from improper handling of token parsing logic within the assembler's macro expansion functionality, where the gpaste_tokens function fails to properly terminate loop iterations under certain conditions. The vulnerability affects the broader assembly toolchain ecosystem and represents a significant concern for developers and system administrators who rely on nasm for compiling assembly code.
The technical implementation of this vulnerability occurs within the gpaste_tokens function which is responsible for managing token pasting operations during macro expansion in the nasm assembler. When processing specific sequences of macro definitions and expansions, the function enters a condition where loop termination criteria are not properly evaluated or updated, leading to an infinite iteration cycle. This flaw can be triggered through carefully constructed assembly code containing recursive macro definitions or complex token manipulation patterns that cause the internal loop structure to never reach its exit condition. The vulnerability operates at the parser level within the assembler's token processing subsystem and demonstrates poor input validation and loop control mechanisms. This type of flaw typically falls under CWE-835, which specifically addresses infinite loops or iterations without proper exit conditions.
From an operational perspective, this vulnerability presents a substantial risk to build environments and automated compilation systems that utilize nasm 2.16rc0. An attacker could exploit this flaw by submitting malicious assembly files containing crafted macro constructs that trigger the infinite loop condition, resulting in resource exhaustion and system unresponsiveness. The impact extends beyond simple denial of service as the infinite loop can consume excessive CPU cycles and memory resources, potentially affecting other processes running on the same system. In continuous integration and deployment pipelines, this vulnerability could cause build failures and system downtime, while in production environments it may lead to service disruption. The vulnerability also represents a potential attack vector for resource exhaustion attacks, where adversaries could repeatedly submit malformed assembly code to consume system resources indefinitely. This aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion.
Mitigation strategies for CVE-2021-45257 should prioritize immediate patching of nasm to versions that address the infinite loop condition in the gpaste_tokens function. System administrators should implement input validation measures to filter potentially malicious assembly code before processing, particularly focusing on macro definitions and token manipulation constructs. Additionally, deployment of resource limits and process timeouts can help contain the impact of exploitation attempts by preventing indefinite resource consumption. Organizations should consider implementing sandboxing mechanisms for assembly code compilation to isolate potentially malicious inputs. Monitoring and logging systems should be enhanced to detect unusual CPU and memory usage patterns that may indicate exploitation attempts. The vulnerability also underscores the importance of proper code review and testing procedures for parser implementations, particularly those handling recursive or iterative operations. Security teams should conduct vulnerability assessments to identify other similar patterns in related software components and ensure that all development environments are updated to patched versions of nasm. This vulnerability serves as a reminder of the critical importance of proper loop termination conditions and input validation in compiler and assembler implementations.