CVE-2021-43573 in RTL8195AM
Summary
by MITRE • 11/11/2021
A buffer overflow was discovered on Realtek RTL8195AM devices before 2.0.10. It exists in the client code when processing a malformed IE length of HT capability information in the Beacon and Association response frame.
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Analysis
by VulDB Data Team • 11/16/2021
The vulnerability identified as CVE-2021-43573 represents a critical buffer overflow condition affecting Realtek RTL8195AM wireless network devices prior to firmware version 2.0.10. This flaw manifests within the device's client code during the processing of malformed information element lengths within HT capability information frames transmitted in beacon and association response packets. The vulnerability resides in the wireless device's handling of IEEE 802.11 management frame structures, specifically targeting the HT (High Throughput) capability information element that defines wireless network parameters including supported data rates, channel width, and transmission modes. The buffer overflow occurs when the device attempts to parse an improperly formatted length field within the HT capability information element, causing memory corruption that can lead to arbitrary code execution or system instability.
This vulnerability operates at the network protocol level and specifically targets the wireless client implementation within embedded Realtek SoC devices. The flaw stems from inadequate input validation and bounds checking within the device's wireless stack when processing management frames from access points. The HT capability information element structure follows IEEE 802.11n standard specifications, but the Realtek implementation fails to properly validate the length field before using it to determine buffer allocation or processing boundaries. This represents a classic buffer overflow vulnerability classified under CWE-121, which describes conditions where insufficient bounds checking allows attackers to write data beyond allocated buffer boundaries, and CWE-787, which addresses out-of-bounds write conditions. The vulnerability can be exploited through specially crafted beacon or association response frames transmitted by a malicious access point within the device's wireless range, making it particularly dangerous in environments where wireless devices are not properly secured against rogue access points.
The operational impact of CVE-2021-43573 extends beyond simple device instability to potentially enable full system compromise and persistent access to affected networks. An attacker positioned within wireless range of vulnerable devices can exploit this vulnerability by transmitting malformed management frames that trigger the buffer overflow condition during normal device operation. Successful exploitation can result in arbitrary code execution with the privileges of the wireless device's operating system, potentially allowing for complete device takeover, data exfiltration, or use as a pivot point for attacks on other network segments. The vulnerability affects embedded IoT devices and wireless clients that rely on Realtek RTL8195AM chipsets, including various smart home devices, industrial sensors, and embedded network equipment that operate in wireless environments. This vulnerability aligns with ATT&CK technique T1059.007, which describes the use of command and scripting interpreters, and T1566.001, which covers the exploitation of wireless network protocols for initial access and lateral movement within targeted environments.
Mitigation strategies for CVE-2021-43573 focus primarily on firmware updates from Realtek and device manufacturers, as the vulnerability requires changes to the wireless stack implementation within the affected devices. Network administrators should immediately prioritize updating all affected Realtek RTL8195AM devices to firmware version 2.0.10 or later, which includes proper bounds checking and input validation for HT capability information elements. Additional defensive measures include implementing wireless network segmentation to limit the impact of compromised devices, deploying intrusion detection systems capable of identifying malformed beacon frames, and configuring wireless access points to enforce strict management frame filtering. Organizations should also consider network monitoring for suspicious wireless activity patterns that may indicate exploitation attempts, particularly around beacon frame structures and association response handling. The vulnerability demonstrates the importance of proper input validation in embedded wireless implementations and highlights the need for comprehensive security testing of network protocol stacks in IoT and embedded systems. Device vendors should implement robust memory safety practices and consider adopting security-by-design principles that incorporate bounds checking and input validation as fundamental components of wireless device firmware development.