CVE-2015-4016 in Steam
Summary
by MITRE
The client detection protocol in Valve Steam allows remote attackers to cause a denial of service (process crash) via a crafted response to a broadcast packet.
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Analysis
by VulDB Data Team • 03/30/2019
The vulnerability identified as CVE-2015-4016 resides within the client detection protocol implementation of Valve Steam, a widely deployed gaming platform and digital distribution system. This flaw represents a classic denial of service vulnerability that specifically targets the network communication mechanisms used by Steam clients to discover and connect with each other on local networks. The vulnerability manifests when a remote attacker crafts and sends a specially formatted response to a broadcast packet that Steam clients routinely send during the discovery process. This crafted response exploits an insufficient input validation mechanism within the Steam client's protocol handling code, causing the application to crash and terminate unexpectedly. The vulnerability is particularly concerning because it operates at the network level and can be exploited without requiring any authentication or prior access to the target system, making it highly accessible to malicious actors.
The technical root cause of this vulnerability stems from improper handling of malformed network responses within the Steam client's broadcast packet processing logic. When a Steam client receives a broadcast packet from another client on the network, it expects a specific format and set of parameters that conform to the established protocol. However, the client detection protocol fails to properly validate the incoming response data before processing it, allowing maliciously crafted payloads to trigger memory corruption or invalid pointer dereferences. This type of vulnerability aligns with CWE-129, which describes improper validation of input ranges, and CWE-787, which covers out-of-bounds write operations. The flaw essentially creates a condition where the Steam client's memory management routines are unable to handle unexpected data structures, leading to process termination. The vulnerability operates within the context of the ATT&CK technique T1498, which involves network denial of service attacks, and demonstrates how client-side protocol implementations can become attack vectors when proper input sanitization is not implemented.
The operational impact of CVE-2015-4016 extends beyond simple service disruption, as it affects the core functionality of Steam's peer-to-peer network discovery mechanism that enables users to find and connect with friends or gaming groups on local networks. When exploited, this vulnerability can cause Steam clients to crash repeatedly, preventing users from accessing the platform's multiplayer features, friend lists, and local game discovery capabilities. The impact is particularly severe in gaming environments where Steam's local network features are frequently used for LAN parties, local multiplayer sessions, or when users attempt to connect with friends in the same network segment. Network administrators and system administrators may observe repeated client crashes, increased system resource consumption due to process restarts, and potential network instability when multiple vulnerable clients exist on the same network segment. The vulnerability affects all versions of Steam client software that implement the problematic detection protocol, making it a widespread concern across the user base. Additionally, the nature of the vulnerability means that it can be exploited in a persistent manner, potentially allowing attackers to maintain ongoing disruption of Steam services on targeted networks.
Mitigation strategies for CVE-2015-4016 primarily focus on both immediate remediation and long-term architectural improvements to prevent similar vulnerabilities from occurring in the future. The most effective immediate solution involves updating to the latest version of Steam client software, which includes patches that properly validate incoming broadcast responses and implement robust error handling mechanisms. Valve addressed this vulnerability through software updates that introduced proper input validation and sanitization routines for all network responses received during the client detection process. Organizations should also implement network monitoring solutions that can detect unusual broadcast traffic patterns or malformed packets that might indicate exploitation attempts. Network segmentation and firewall rules can be configured to limit broadcast traffic between Steam clients, reducing the attack surface and providing additional protection layers. From a security architecture perspective, this vulnerability highlights the importance of implementing defensive programming practices such as bounds checking, input validation, and proper error handling in all network-facing applications. The remediation process should also include comprehensive testing of protocol implementations to ensure that they can gracefully handle unexpected inputs without crashing or corrupting system resources. Security teams should consider implementing intrusion detection systems that can identify and alert on suspicious network behavior related to Steam client protocols, providing early warning capabilities for potential exploitation attempts.