CVE-2021-33466 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_smacro() in modules/preprocs/nasm/nasm-pp.c.
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Analysis
by VulDB Data Team • 08/27/2022
The vulnerability identified as CVE-2021-33466 represents a critical NULL pointer dereference flaw within the yasm assembler version 1.3.0. This issue specifically manifests within the expand_smacro() function located in the modules/preprocs/nasm/nasm-pp.c file, where the software fails to properly validate pointer references during macro expansion processes. The yasm assembler serves as a crucial component in the software development pipeline for generating machine code from assembly language sources, making this vulnerability particularly concerning for developers and security professionals who rely on this toolchain for building software systems. The flaw occurs when the assembler encounters certain macro constructs that trigger the expansion routine without proper initialization of required data structures, leading to a runtime crash when the code attempts to dereference a null pointer.
This vulnerability directly maps to CWE-476 which defines NULL Pointer Dereference as a condition where a null pointer is dereferenced, causing a program to crash or potentially allowing for more sophisticated attacks depending on the execution context. The operational impact of this vulnerability extends beyond simple program termination, as it can be exploited by malicious actors to disrupt build processes or potentially escalate privileges if the assembler is invoked with elevated permissions during software compilation. The flaw demonstrates a classic software engineering oversight where proper input validation and pointer initialization checks were omitted during the development of the macro processing functionality, creating an exploitable condition that can be triggered through carefully crafted assembly source files containing malformed macro definitions.
The attack surface for this vulnerability encompasses any system utilizing yasm version 1.3.0 for assembly code processing, particularly affecting software development environments, continuous integration pipelines, and build servers where automated compilation processes might be exposed to untrusted input. From an attack perspective, this vulnerability aligns with ATT&CK technique T1059.001 which covers command and script injection, as the exploitation could occur through malicious assembly code that triggers the vulnerable code path. The issue is particularly dangerous in automated environments where build systems might automatically process assembly files from untrusted sources without proper sanitization, potentially allowing attackers to cause denial of service conditions or disrupt legitimate development workflows.
Mitigation strategies for CVE-2021-33466 should prioritize immediate upgrading to yasm version 1.3.1 or later, which contains the necessary patches to address the NULL pointer dereference issue. Organizations should also implement defensive programming practices such as input sanitization and validation for all assembly source files processed through the yasm toolchain, ensuring that macro definitions are properly validated before execution. Additionally, system administrators should monitor build processes for abnormal termination patterns that might indicate exploitation attempts, and consider implementing sandboxing mechanisms for assembly code processing to limit potential impact. The vulnerability underscores the importance of thorough code review processes and proper memory management practices in compiler and assembler toolchains, particularly when handling user-supplied input that may trigger complex processing routines.