2025/06 : Internal-CISA - Microsoft Windows - CVE-2025-21418

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This article provides an in-depth analysis of the Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability, identified as CVE-2025-21418. This high-severity vulnerability, recently added to the CISA Known Exploited Vulnerabilities Catalog, poses a significant risk to systems running Microsoft Windows. Understanding the nature of this vulnerability, its potential impact, and available mitigation strategies is crucial for maintaining a secure computing environment. This document aims to offer a comprehensive overview of CVE-2025-21418, drawing upon information from CISA and the National Vulnerability Database (NVD), to help system administrators and security professionals effectively address this threat. The article will delve into the specifics of the vulnerability, its severity level, the affected systems, and the recommended steps for remediation, ensuring that readers are well-equipped to protect their infrastructure. The criticality of addressing this vulnerability cannot be overstated, given its potential for exploitation and the severe consequences that could arise from successful attacks. Therefore, this analysis serves as a vital resource for organizations striving to bolster their cybersecurity posture and mitigate the risks associated with this actively exploited vulnerability. Furthermore, the information presented here will enable a proactive approach to security management, ensuring that systems are patched and secured against potential exploits. We will also explore the broader context of the vulnerability within the landscape of cybersecurity threats, highlighting its significance and the importance of continuous monitoring and vigilance.

Vulnerability Summary

The Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability, identified as CVE-2025-21418, is a critical security flaw affecting various Windows operating systems. This vulnerability resides within the Windows Ancillary Function Driver (AFD) for WinSock, a core component responsible for handling network communications. A heap-based buffer overflow occurs when a program writes data beyond the allocated memory buffer on the heap, leading to potential system instability, crashes, or, more critically, arbitrary code execution. This particular vulnerability allows an attacker to potentially elevate their privileges on the system, gaining unauthorized access and control. The inclusion of CVE-2025-21418 in the CISA Known Exploited Vulnerabilities Catalog underscores its active exploitation in the wild, making it an immediate concern for organizations using affected Windows versions. The severity of this vulnerability is further highlighted by its CVSS score, which indicates a high level of risk. Mitigation efforts are crucial to prevent potential exploitation and safeguard systems against malicious attacks. This section will also cover the technical details of the vulnerability, including the specific conditions under which it can be exploited, and the potential attack vectors that malicious actors might employ. Understanding these aspects is essential for developing effective defense strategies and ensuring the timely application of security patches. The discussion will also touch upon the broader implications of buffer overflow vulnerabilities in operating systems and the importance of secure coding practices to prevent such flaws.

Reference

This analysis draws upon information from the Cybersecurity and Infrastructure Security Agency (CISA) Known Exploited Vulnerabilities Catalog, a trusted source for identifying vulnerabilities actively exploited in the wild. The reference link provided (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) directs users to the official CISA catalog entry for CVE-2025-21418, offering up-to-date information and guidance. Additionally, the National Vulnerability Database (NVD) entry for CVE-2025-21418 (https://nvd.nist.gov/vuln/detail/CVE-2025-21418) provides a comprehensive overview of the vulnerability, including its technical details, impact, and affected systems. Consulting these authoritative sources is essential for staying informed about the latest developments and ensuring the accuracy of vulnerability assessments and mitigation efforts. These references serve as foundational resources for cybersecurity professionals and system administrators, offering critical insights into the nature and severity of CVE-2025-21418. Leveraging these resources is a best practice in vulnerability management, allowing for a more informed and proactive approach to security. The availability of detailed information from CISA and NVD empowers organizations to effectively prioritize and address vulnerabilities, thereby reducing their exposure to potential cyber threats. Furthermore, these databases often include specific guidance on remediation and mitigation, making them invaluable tools for maintaining a secure IT infrastructure. The continued reliance on such reputable sources is paramount in the ever-evolving landscape of cybersecurity.

Severity

The Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability (CVE-2025-21418) has been assigned a HIGH severity rating, based on the Common Vulnerability Scoring System (CVSS) v3.1. The CVSS score is (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H), indicating the potential for significant impact. Let's break down this score to understand the severity in detail:

  • AV:L (Attack Vector: Local): This means an attacker needs local access to the system to exploit the vulnerability. While this limits the attack surface compared to remote vulnerabilities, it still poses a serious threat if an attacker has already gained a foothold on the system.
  • AC:L (Attack Complexity: Low): The vulnerability is easy to exploit, requiring minimal technical skill or specific conditions to be met. This increases the likelihood of successful exploitation.
  • PR:L (Privileges Required: Low): An attacker with low-level privileges can exploit this vulnerability. This means that even a standard user account can be used to trigger the vulnerability, making it easier for attackers to escalate their privileges.
  • UI:N (User Interaction: None): No user interaction is required to exploit the vulnerability. This allows an attacker to exploit the vulnerability without any user intervention, making it more dangerous.
  • S:U (Scope: Unchanged): The vulnerability exploitation does not affect resources beyond the security scope managed by the security authority. However, it can still lead to significant damage within the affected system.
  • C:H (Confidentiality: High): Successful exploitation can lead to a complete loss of confidentiality, allowing the attacker to access sensitive information.
  • I:H (Integrity: High): The vulnerability can lead to a complete loss of integrity, allowing the attacker to modify system files and data.
  • A:H (Availability: High): Exploitation can result in a complete loss of system availability, causing a denial-of-service condition.

The high CVSS score and the detailed breakdown clearly indicate the critical nature of this vulnerability. Organizations must prioritize patching and mitigation efforts to protect their systems. The combination of local attack vector, low complexity, and the potential for high impact on confidentiality, integrity, and availability makes this vulnerability a significant concern. Furthermore, the fact that it requires only low privileges and no user interaction makes it even more dangerous, as attackers can easily exploit it once they have gained minimal access to the system.

Detailed Description of the Vulnerability

The Microsoft Windows Ancillary Function Driver (AFD) for WinSock Elevation of Privilege Vulnerability, designated as CVE-2025-21418, stems from a heap-based buffer overflow within the AFD driver. This driver is a crucial component of the Windows networking stack, responsible for handling various network-related functions and communications. A buffer overflow occurs when a program attempts to write data beyond the allocated buffer's boundaries. In the case of a heap-based buffer overflow, this occurs on the heap, a region of memory used for dynamic memory allocation. Attackers can exploit this vulnerability by sending specially crafted network packets or triggering specific system calls that cause the AFD driver to write data beyond the allocated buffer. This overflow can overwrite adjacent memory regions, potentially corrupting critical system data or injecting malicious code. If successful, an attacker can elevate their privileges to SYSTEM, the highest privilege level in Windows, allowing them to gain complete control over the affected system. This can lead to a wide range of malicious activities, including installing malware, stealing sensitive data, or disrupting system operations. The technical details of the vulnerability are complex and involve understanding the intricacies of the AFD driver's memory management and data handling processes. Exploiting this vulnerability typically requires a deep understanding of Windows internals and the ability to craft specific payloads that trigger the overflow. However, the existence of public exploits and the active exploitation of this vulnerability in the wild demonstrate that it is a viable attack vector for malicious actors. Therefore, a thorough understanding of the vulnerability's mechanisms and potential impact is essential for developing effective mitigation strategies and ensuring system security. The severity of this vulnerability is compounded by the fact that it can be exploited with only low-level privileges and without any user interaction, making it a potent tool for attackers.

Reporter

This vulnerability was reported by the Cybersecurity and Infrastructure Security Agency (CISA), a United States federal agency responsible for protecting the nation’s critical infrastructure from physical and cyber threats. CISA's involvement highlights the significance and potential impact of CVE-2025-21418. CISA's mission includes identifying and mitigating vulnerabilities that could be exploited by malicious actors, and their reporting of this vulnerability underscores its critical nature. CISA's expertise and resources are instrumental in disseminating vital security information and coordinating responses to cyber incidents. Their alert about CVE-2025-21418 serves as a call to action for organizations to promptly address this vulnerability and safeguard their systems. The fact that CISA has flagged this vulnerability emphasizes the urgency and importance of implementing the necessary security measures. CISA's role as a trusted source of cybersecurity information and guidance makes their reports particularly significant for organizations seeking to maintain a robust security posture. Their involvement in identifying and reporting vulnerabilities such as CVE-2025-21418 helps to protect critical infrastructure and ensure the resilience of the nation's digital assets. CISA's ongoing efforts to collaborate with industry partners and government agencies are crucial for effectively addressing the ever-evolving landscape of cyber threats. Their work in promoting cybersecurity awareness and best practices plays a vital role in safeguarding the digital ecosystem.

In conclusion, the Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability (CVE-2025-21418) represents a significant security risk that demands immediate attention. The high severity rating, coupled with its active exploitation in the wild, necessitates a proactive approach to mitigation. Organizations must prioritize patching affected systems and implementing recommended security measures to prevent potential attacks. The information presented in this analysis, drawing upon authoritative sources such as CISA and NVD, provides a comprehensive understanding of the vulnerability, its potential impact, and the steps required for remediation. The critical nature of this vulnerability cannot be overstated, and delaying mitigation efforts can lead to severe consequences, including data breaches, system compromise, and operational disruptions. Therefore, it is imperative that system administrators and security professionals take swift action to address this threat. The ongoing vigilance and monitoring of systems for potential vulnerabilities are essential components of a robust cybersecurity strategy. The dynamic nature of the threat landscape requires a continuous commitment to security best practices and the prompt application of security updates. By staying informed about emerging threats and proactively addressing vulnerabilities, organizations can significantly reduce their risk exposure and maintain a secure computing environment. The insights provided in this article serve as a valuable resource for organizations seeking to strengthen their cybersecurity posture and protect their digital assets from malicious attacks. The commitment to security must be a continuous process, ensuring that systems are regularly assessed, patched, and monitored for potential vulnerabilities. This proactive approach is the most effective way to mitigate the risks associated with CVE-2025-21418 and other emerging threats.