CVE-2017-10868 in H2O
Summary
by MITRE
H2O version 2.2.2 and earlier allows remote attackers to cause a denial of service in the server via specially crafted HTTP/1 header.
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Analysis
by VulDB Data Team • 01/18/2023
The vulnerability identified as CVE-2017-10868 affects H2O web server versions 2.2.2 and earlier, presenting a significant security risk that enables remote attackers to execute denial of service attacks through crafted HTTP/1 headers. This flaw represents a critical weakness in the server's request handling mechanism that can be exploited without authentication, making it particularly dangerous in production environments where availability of services is paramount. The vulnerability stems from insufficient validation of HTTP headers during the request processing phase, allowing malicious actors to construct specific header sequences that cause the server to consume excessive resources or crash entirely.
The technical implementation of this vulnerability involves the improper parsing and handling of HTTP/1 headers within the H2O server software. When the server receives a specially crafted header sequence, it fails to properly validate the header content, leading to resource exhaustion or unexpected behavior that results in service disruption. This type of flaw typically falls under CWE-129, which encompasses improper validation of input, and specifically relates to CWE-20, which covers input validation issues that can lead to resource exhaustion. The vulnerability demonstrates characteristics consistent with buffer overflows or memory corruption patterns where malformed input causes the server process to behave unpredictably, often resulting in process termination or indefinite resource consumption.
From an operational perspective, this vulnerability poses substantial risk to organizations relying on H2O for web serving operations, as it can be exploited to render services unavailable to legitimate users without requiring any privileged access or credentials. The impact extends beyond simple service interruption, as it can affect business continuity and potentially provide attackers with opportunities to conduct further reconnaissance or launch additional attacks. The vulnerability's exploitation is relatively straightforward, requiring only basic HTTP header crafting capabilities, which makes it particularly dangerous in environments where the server is exposed to untrusted networks or public internet access. Organizations using vulnerable versions of H2O may experience cascading failures if the server becomes unresponsive, potentially affecting dependent services and systems that rely on its availability.
The mitigation strategy for this vulnerability involves immediate patching of affected H2O installations to versions that contain proper header validation and resource limiting mechanisms. Organizations should also implement network-level protections such as rate limiting and header filtering to reduce the impact of potential exploitation attempts. Additionally, monitoring systems should be enhanced to detect unusual patterns in HTTP header usage that might indicate exploitation attempts. From a defensive standpoint, this vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service, and demonstrates the importance of implementing proper input validation as a fundamental security control. The incident also highlights the need for regular security assessments and patch management processes to prevent exploitation of known vulnerabilities in widely deployed software components.