CVE-2023-31973 in yasm
Summary
by MITRE • 05/09/2023
yasm v1.3.0 was discovered to contain a use after free via the function expand_mmac_params at /nasm/nasm-pp.c. Note: Multiple third parties dispute this as a bug and not a vulnerability according to the YASM security policy.
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Analysis
by VulDB Data Team • 12/30/2025
The vulnerability identified as CVE-2023-31973 affects yasm version 1.3.0 and involves a use-after-free condition within the expand_mmac_params function located in the nasm/nasm-pp.c source file. This type of vulnerability represents a critical memory safety issue that can potentially lead to arbitrary code execution or system compromise when the affected software processes malformed input. The use-after-free flaw occurs when a program continues to reference memory after it has been freed, creating opportunities for attackers to manipulate memory contents or trigger exploitable conditions. The vulnerability specifically manifests in the preprocessor component of yasm, which is responsible for processing assembly language source files before compilation. When the expand_mmac_params function handles certain input parameters, it fails to properly manage memory allocation and deallocation sequences, leaving potential for memory corruption that could be exploited by malicious actors.
This vulnerability falls under the CWE-416 category of Use After Free, which is classified as a memory safety issue in the Common Weakness Enumeration system. The operational impact of this flaw extends beyond simple memory corruption, as it can enable attackers to execute arbitrary code with the privileges of the affected application. The yasm assembler is commonly used in build systems and development environments, making it a potential target for supply chain attacks or exploitation in automated build processes. The vulnerability's exploitation potential is heightened by the fact that it occurs within a preprocessor function that processes input from assembly source files, which could be manipulated by untrusted users or malicious actors. Attackers could craft specific assembly code that triggers the use-after-free condition when yasm processes these inputs, potentially leading to privilege escalation or complete system compromise.
The security implications of CVE-2023-31973 extend to various operational contexts where yasm is employed as part of software development or build infrastructure. Development environments that utilize yasm for assembling code, automated build systems, and continuous integration pipelines could all be at risk if they process untrusted assembly input. The vulnerability's classification as a use-after-free makes it particularly concerning for applications that handle user-provided input or operate in multi-user environments where input validation is critical. According to the ATT&CK framework, this vulnerability could be leveraged as part of a broader attack chain under techniques such as T1059.001 for command and scripting interpreter and T1583.001 for adversary infrastructure. The exploitation of this flaw could potentially enable attackers to establish persistent access or escalate privileges within systems where yasm is installed and used.
Organizations should consider immediate mitigation strategies including updating to patched versions of yasm or implementing input validation measures to prevent exploitation of this vulnerability. The disputed nature of this vulnerability according to YASM security policy suggests that organizations should carefully evaluate their risk exposure and determine whether the specific use cases of yasm in their environments warrant additional protective measures. Security teams should monitor for any exploitation attempts targeting this vulnerability and consider implementing runtime protections or sandboxing measures for systems that process assembly code through yasm. The vulnerability demonstrates the importance of proper memory management in software development and highlights the need for comprehensive security testing including memory safety validation. Organizations should also review their build processes and ensure that assembly code inputs are properly sanitized and validated before being processed by yasm or similar tools.