CVE-2021-33455 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 do_directive() in modules/preprocs/nasm/nasm-pp.c.
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Analysis
by VulDB Data Team • 07/26/2022
The vulnerability identified as CVE-2021-33455 represents a critical null pointer dereference flaw within the yasm assembler version 1.3.0. This issue manifests specifically within the do_directive() function located in the modules/preprocs/nasm/nasm-pp.c source file. The yasm assembler is widely utilized in software development environments for converting assembly language source code into object files, making it a critical component in the build processes of numerous applications and systems. The flaw occurs during the processing of preprocessor directives, which are essential for conditional compilation and macro expansion in assembly code.
The technical implementation of this vulnerability stems from inadequate input validation and error handling within the directive processing mechanism. When the do_directive() function encounters certain malformed or unexpected preprocessor directives, it attempts to dereference a null pointer without proper null checks. This programming error falls under the category of CWE-476_NULL_Pointer_Dereference, which is classified as a common weakness in software development practices. The absence of proper null pointer validation creates a scenario where the application crashes or terminates unexpectedly when processing malicious or malformed input, leading to potential denial of service conditions.
The operational impact of this vulnerability extends beyond simple application instability, as it can be exploited by adversaries to disrupt legitimate build processes and development workflows. Attackers could craft malicious assembly source files containing specially crafted preprocessor directives that trigger the null pointer dereference, causing the yasm assembler to crash and potentially preventing successful compilation of software projects. This vulnerability is particularly concerning in environments where automated build systems rely on yasm for assembly processing, as it could be leveraged to cause widespread disruption of development pipelines and software delivery processes. The flaw also aligns with ATT&CK technique T1499.004_Compromise_of_Utilities_and_Systems, where adversaries target commonly used system utilities to create persistent denial of service conditions.
Mitigation strategies for this vulnerability require immediate patching of the yasm assembler to version 1.3.1 or later, which contains the necessary fixes for the null pointer dereference issue. System administrators and development teams should conduct comprehensive vulnerability assessments to identify any systems running the affected version of yasm and ensure prompt remediation. Additionally, implementing input validation measures and sandboxing techniques for assembly code processing can provide additional layers of protection. Organizations should also consider monitoring build systems for unusual patterns of assembler crashes or failures, as these could indicate exploitation attempts. The fix implemented in the patched version addresses the root cause by introducing proper null pointer checks and robust error handling within the directive processing functions, thereby preventing the crash condition that previously occurred when encountering malformed preprocessor directives.