CVE-2019-15944 in Counter-Strike: Global Offensive
Summary
by MITRE
In Counter-Strike: Global Offensive before 8/29/2019, community game servers can display unsafe HTML in a disconnection message.
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Analysis
by VulDB Data Team • 12/13/2023
The vulnerability CVE-2019-15944 represents a cross-site scripting weakness in Counter-Strike: Global Offensive that existed prior to the August 29, 2019 update. This flaw allowed malicious community game servers to inject unsafe HTML content into disconnection messages that were displayed to players, creating a potential vector for user interaction with malicious code. The issue stems from insufficient input sanitization within the game's client-side rendering of server-generated disconnection notifications, which directly violates security principles outlined in CWE-79 - Cross-site Scripting. The vulnerability operates at the application layer where user-supplied data is not properly escaped or validated before being rendered in the client interface, making it susceptible to exploitation by attackers who control game servers.
The technical execution of this vulnerability relies on the game client's handling of HTML content within server-generated messages, particularly during disconnection events when players receive notifications about their session termination. When a player disconnects from a malicious server, the client displays a message that includes unfiltered HTML content, allowing attackers to inject script tags or other malicious elements that could execute within the context of the game client. This represents a classic client-side XSS attack vector that can potentially lead to session hijacking, data exfiltration, or further exploitation of the gaming environment. The vulnerability specifically impacts community servers that lack proper security controls, as opposed to official valve servers which would have more robust input validation mechanisms.
From an operational standpoint, this vulnerability creates significant risks for players who may unknowingly interact with malicious content while disconnecting from game servers. The impact extends beyond simple phishing attempts to potentially enable more sophisticated attacks such as credential theft or malware distribution through the game client interface. Players who encounter these malicious disconnection messages may inadvertently execute code that could compromise their system or account credentials, particularly if they interact with the displayed content through mouse clicks or other user actions. The attack surface is particularly concerning because it leverages the trust relationship between players and game servers, exploiting the expectation that disconnection messages are benign notifications rather than potential attack vectors.
Mitigation strategies for this vulnerability should focus on implementing proper input sanitization and output encoding within the game client's message rendering system. The most effective approach involves ensuring that all server-generated content is properly escaped before display, particularly HTML content that may contain script tags or other executable elements. Security measures should include validation of message content to prevent the inclusion of unsafe HTML tags and attributes, as well as implementing Content Security Policy headers where applicable. Additionally, game developers should consider implementing server-side validation to prevent malicious content from being submitted to client systems in the first place, aligning with ATT&CK technique T1211 - Exploitation for Defense Evasion. Players should be advised to avoid community servers with questionable reputations and to remain vigilant when encountering unusual disconnection messages that prompt for user interaction, as this vulnerability demonstrates the importance of proper input validation in client-side applications.