CVE-2021-30481 in Steam
Summary
by MITRE • 04/11/2021
Valve Steam before 2021-04-17, when a Source engine game is installed, allows remote authenticated users to execute arbitrary code because of a buffer overflow that occurs for a Steam invite after one click.
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Analysis
by VulDB Data Team • 11/03/2025
The vulnerability identified as CVE-2021-30481 represents a critical buffer overflow flaw within the Valve Steam client software that affected versions prior to the 2021-04-17 release. This security weakness specifically targets Source engine games installed on affected systems and creates a pathway for remote authenticated attackers to execute arbitrary code. The vulnerability manifests through a carefully crafted Steam invite mechanism that, when clicked by a victim, triggers the buffer overflow condition within the Steam client's processing logic.
The technical implementation of this flaw involves improper input validation within the Steam client's handling of invite data structures. When a user clicks on a malicious Steam invite link, the client processes the invite parameters without adequate bounds checking, allowing an attacker to overflow a fixed-size buffer in memory. This buffer overflow occurs in the context of the Steam client process, which typically runs with elevated privileges due to its role in managing game installations and updates. The vulnerability falls under the CWE-121 buffer overflow category, specifically manifesting as a stack-based buffer overflow that can be exploited to overwrite adjacent memory locations and potentially redirect program execution flow.
The operational impact of CVE-2021-30481 extends beyond simple code execution, as it enables attackers to gain unauthorized access to systems running vulnerable Steam installations. This vulnerability operates within the ATT&CK framework under the T1059.007 technique category, specifically targeting application execution through legitimate system processes. The exploit requires only a single click from a victim, making it particularly dangerous as it leverages social engineering tactics to deliver malicious payloads. Attackers can craft invite links that contain specially formatted data designed to overflow the buffer and inject malicious code, potentially allowing them to install malware, access sensitive system information, or establish persistent access to compromised machines.
Mitigation strategies for this vulnerability include immediate installation of the Steam client update released on April 17, 2021, which patched the buffer overflow condition by implementing proper input validation and bounds checking. Organizations should also implement network-level controls to monitor for suspicious Steam invite traffic and consider deploying endpoint protection solutions that can detect anomalous behavior patterns associated with buffer overflow exploitation attempts. The vulnerability demonstrates the importance of maintaining up-to-date software versions and highlights the risks associated with click-based attack vectors in gaming platforms. Security teams should also consider implementing user education programs to raise awareness about the dangers of clicking unknown Steam invites, as this vulnerability specifically requires user interaction to be exploited successfully.