CVE-2021-33457 in yasm
Summary
by MITRE • 07/26/2022
An issue was discovered in yasm version 1.3.0. There is a NULL pointer dereference in expand_mmac_params() in modules/preprocs/nasm/nasm-pp.c.
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Analysis
by VulDB Data Team • 07/26/2022
The vulnerability identified as CVE-2021-33457 represents a critical NULL pointer dereference flaw within the yasm assembler version 1.3.0. This issue specifically manifests in the expand_mmac_params() function located within the modules/preprocs/nasm/nasm-pp.c source file. The yasm project serves as a portable and completely open-source macro assembler that supports the x86 and x86-64 instruction sets, making it a widely used component in software development and build systems across various platforms and applications.
The technical flaw stems from inadequate input validation and error handling within the expand_mmac_params() function which processes macro parameters for the nasm preprocessor module. When the assembler encounters specific malformed or unexpected input patterns during macro expansion, the function fails to properly check for NULL pointer conditions before attempting to dereference memory addresses. This NULL pointer dereference vulnerability occurs during the preprocessing phase of assembly compilation, where the tool processes macro definitions and parameter expansions before generating machine code. The absence of proper null checks creates a condition where the program attempts to access memory at address zero, leading to an immediate crash and potential system instability.
The operational impact of this vulnerability extends beyond simple application crashes, as it presents a significant security risk within build environments and automated compilation systems. Attackers could potentially exploit this weakness by crafting malicious input files or macro definitions that trigger the NULL pointer dereference during the assembly process. This could result in denial of service conditions affecting legitimate build processes, particularly in continuous integration environments where automated compilation pipelines rely on yasm for code generation. The vulnerability affects systems where yasm is used as a preprocessing tool, including software development environments, cross-compilation toolchains, and embedded system build processes that depend on this assembler for code generation.
From a cybersecurity perspective, this vulnerability aligns with CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations. The flaw demonstrates poor defensive programming practices and highlights the importance of robust input validation and error handling mechanisms in security-critical software components. The ATT&CK framework categorizes this issue under software development practices and build system vulnerabilities, where adversaries might leverage such weaknesses to disrupt development workflows or potentially escalate privileges in compromised environments. Organizations using yasm in their build infrastructure should consider this vulnerability as part of their broader security posture assessment, particularly in environments where build systems are exposed to untrusted input sources or where the assembler is used in automated security testing frameworks.
Mitigation strategies for CVE-2021-33457 should prioritize immediate patching of yasm installations to versions that address the NULL pointer dereference issue. System administrators and developers should also implement input validation measures for any macro files or assembly code processed through yasm, including sanitization of user-supplied input and monitoring for unusual preprocessing patterns. Additionally, organizations should consider implementing sandboxing or containerization techniques for assembly processing tasks to limit potential impact from exploitation attempts. Regular security assessments of build environments and dependency management practices should include verification of yasm versions and their vulnerability status to prevent exploitation of similar issues in other components of the software supply chain.