CVE-2016-4817 in H2O
Summary
by MITRE
lib/http2/connection.c in H2O before 1.7.3 and 2.x before 2.0.0-beta5 mishandles HTTP/2 disconnection, which allows remote attackers to cause a denial of service (use-after-free and application crash) or possibly execute arbitrary code via a crafted packet.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 08/24/2022
The vulnerability identified as CVE-2016-4817 affects the H2O HTTP/2 server implementation and represents a critical security flaw in how the software handles HTTP/2 connection termination. This issue exists in versions prior to 1.7.3 and 2.x versions before 2.0.0-beta5, making it a widespread concern for systems utilizing this popular open-source HTTP server. The flaw manifests in the lib/http2/connection.c file where improper handling of HTTP/2 disconnection sequences creates exploitable conditions that can lead to severe consequences including application crashes and potential code execution.
The technical root cause of this vulnerability lies in the improper memory management during HTTP/2 connection termination processes. When a client disconnects from an H2O server using HTTP/2, the server fails to properly manage the memory associated with the connection state, leading to use-after-free conditions where freed memory locations are still accessed by subsequent operations. This memory corruption vulnerability is classified under CWE-416 as use-after-free, which occurs when a program continues to reference memory after it has been freed, potentially allowing attackers to manipulate program execution flow. The flaw specifically impacts the HTTP/2 connection management logic where connection state cleanup does not properly account for all active references to connection resources.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially enable remote code execution, making it particularly dangerous for web servers exposed to the internet. Attackers can craft malicious HTTP/2 packets that trigger the flawed disconnection handling, causing the H2O server to crash or potentially execute arbitrary code with the privileges of the running process. This vulnerability affects the availability and integrity of web services, as successful exploitation can lead to complete service disruption or unauthorized access to server resources. The use-after-free condition creates a vector for attackers to potentially manipulate memory contents and redirect program execution, representing a significant compromise to system security.
Organizations running affected versions of H2O should prioritize immediate patching to address this vulnerability, as the potential for remote code execution makes it a high-priority security concern. The recommended mitigation involves upgrading to H2O version 1.7.3 or later 2.x versions 2.0.0-beta5 and beyond, where the HTTP/2 connection handling has been properly corrected to prevent memory management issues during disconnection. Security teams should also implement monitoring for unusual connection patterns and ensure proper network segmentation to limit potential attack surface. This vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and T1059 for command and scripting interpreter, as exploitation could enable both service disruption and remote command execution capabilities. The flaw demonstrates the importance of proper memory management in network services and highlights how seemingly minor issues in connection handling can lead to critical security vulnerabilities.