CVE-2017-10908 in H2O
Summary
by MITRE
H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via specially crafted HTTP/2 header.
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Analysis
by VulDB Data Team • 01/18/2023
The vulnerability identified as CVE-2017-10908 affects H2O web server versions 2.2.3 and earlier, presenting a significant denial of service risk that can be exploited remotely by attackers. This issue specifically targets the HTTP/2 implementation within the H2O server, which is widely used for high-performance web serving and reverse proxying. The vulnerability stems from insufficient validation of HTTP/2 headers, allowing malicious actors to craft specially formatted headers that trigger unexpected behavior in the server's processing logic. This flaw represents a critical security gap in the server's protocol handling capabilities, potentially enabling attackers to disrupt service availability for legitimate users.
The technical flaw manifests in the server's inability to properly handle malformed or specially crafted HTTP/2 headers during the connection establishment or data transmission phases. When the H2O server receives these maliciously constructed headers, it fails to process them gracefully and instead enters a state where it becomes unresponsive or crashes entirely. This occurs because the server's HTTP/2 implementation lacks adequate input sanitization and error handling mechanisms for header validation. The vulnerability is particularly dangerous as it can be exploited without authentication, making it accessible to any remote attacker who can establish a connection to the vulnerable server. The flaw typically results in the server process terminating unexpectedly or consuming excessive resources, leading to complete service disruption.
The operational impact of this vulnerability extends beyond simple service interruption, as it can affect organizations relying on H2O for critical web services including API endpoints, web applications, and reverse proxy configurations. Attackers can leverage this vulnerability to perform sustained denial of service attacks against web applications, potentially causing significant business disruption and financial loss. The attack surface is particularly broad since H2O is commonly deployed in cloud environments, microservices architectures, and high-traffic web applications where maintaining uptime is crucial. Organizations using vulnerable versions may experience extended downtime while implementing patches, potentially affecting user experience and service level agreements. The vulnerability also increases the risk of cascading failures in environments where H2O is used as a reverse proxy for multiple backend services.
Security practitioners should immediately upgrade to H2O version 2.2.4 or later, which contains the necessary fixes for this vulnerability. The mitigation strategy involves not only applying the vendor-provided patch but also implementing network-level protections such as rate limiting and connection monitoring to detect potential exploitation attempts. Organizations should conduct thorough testing of the updated software to ensure compatibility with existing configurations and monitor for any unusual connection patterns or resource consumption that might indicate exploitation attempts. Additionally, implementing proper input validation and sanitization at the network level can provide defense-in-depth protection against similar vulnerabilities. This vulnerability aligns with CWE-20, which addresses improper input validation, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks, emphasizing the need for comprehensive security controls to protect against such threats.