CVE-2021-1699 in Windows
Summary
by MITRE • 01/13/2021
Windows (modem.sys) Information Disclosure Vulnerability
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Analysis
by VulDB Data Team • 10/09/2024
This vulnerability resides within the Windows modem.sys driver component which handles communication with modem devices and related hardware interfaces. The issue represents a critical information disclosure flaw that allows unauthorized access to sensitive kernel-mode memory structures. The vulnerability manifests when the system processes certain IOCTL (Input/Output Control) requests through the modem driver interface, specifically affecting how the driver manages memory allocation and data handling during modem communication sessions. Attackers can exploit this weakness to read arbitrary kernel memory locations, potentially exposing confidential system information including credentials, encryption keys, or other sensitive data stored in protected memory regions.
The technical root cause stems from improper validation of input parameters within the modem.sys driver's handling of device control requests. When malicious actors submit crafted IOCTL commands with malformed parameters, the driver fails to properly sanitize these inputs before processing them, leading to information leakage through memory read operations. This vulnerability specifically impacts the Windows operating system versions that include the modem.sys driver, particularly those running on x86 and x64 architectures where the driver executes with elevated privileges. The flaw aligns with CWE-200, which categorizes information exposure vulnerabilities, and represents a classic example of insufficient input validation leading to memory disclosure attacks.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates potential pathways for further exploitation within the Windows kernel environment. An attacker who successfully exploits this vulnerability could gain access to sensitive system information that might aid in subsequent attacks, including privilege escalation attempts or targeted exploitation of other system components. The vulnerability's presence in the modem.sys driver means that even systems that do not actively use modem hardware remain at risk, as the driver remains loaded in memory and accessible through legitimate system interfaces. This makes the attack surface broader than typical driver-based vulnerabilities, as the exploitation does not require specific hardware interaction.
Security professionals should implement immediate mitigations including applying the relevant Microsoft security updates that address this vulnerability through proper input validation and memory handling improvements within the modem.sys driver. Organizations should also consider implementing runtime protection measures such as kernel-mode exploit prevention tools and monitoring for suspicious IOCTL activity patterns. The vulnerability demonstrates the importance of driver security hardening and proper input validation across all system components, particularly those operating at kernel level where information disclosure can have severe implications for overall system security. Network administrators should monitor for unusual modem-related activity or system calls that might indicate exploitation attempts, while system administrators should ensure that all Windows systems receive timely security patches to prevent potential exploitation. This vulnerability serves as a reminder of the critical nature of kernel-mode driver security and the potential for seemingly benign components to create significant security risks when not properly validated and secured against malicious input.