CVE-2016-4864 in H2O
Summary
by MITRE
H2O versions 2.0.3 and earlier and 2.1.0-beta2 and earlier allows remote attackers to cause a denial-of-service (DoS) via format string specifiers in a template file via fastcgi, mruby, proxy, redirect or reproxy.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2016-4864 affects the H2O web server software, specifically versions 2.0.3 and earlier, as well as 2.1.0-beta2 and earlier releases. This security flaw represents a significant concern for web server administrators and security professionals due to its potential to disrupt service availability. The vulnerability stems from improper handling of format string specifiers within template files when processing requests through various fastcgi, mruby, proxy, redirect, or reproxy mechanisms. The affected H2O versions demonstrate a critical weakness in input validation and string processing that can be exploited by remote attackers to execute malicious code or cause system instability.
The technical exploitation of this vulnerability occurs when an attacker crafts malicious template files containing format string specifiers that are then processed by the H2O server. These format specifiers, when improperly handled during template rendering, can lead to memory corruption, stack manipulation, or arbitrary code execution depending on the specific implementation details. The vulnerability affects multiple processing pathways within the H2O server including fastcgi integration, mruby scripting capabilities, proxy forwarding mechanisms, redirect handling, and reproxy functionality. This widespread impact across different server modules indicates a fundamental flaw in the input sanitization process rather than a localized issue within a single component.
From an operational perspective, this vulnerability presents a severe denial-of-service risk that can compromise the availability of web services hosted on affected H2O servers. Attackers can leverage this flaw to crash the web server process, causing temporary or prolonged unavailability of websites and applications. The remote nature of the attack means that systems can be compromised from anywhere on the internet without requiring local access or authentication. The vulnerability's impact extends beyond simple service disruption as it may potentially allow for more sophisticated attacks including privilege escalation or information disclosure depending on the server configuration and underlying system architecture. Organizations relying on H2O for web hosting, API gateways, or reverse proxy services face significant risk exposure.
The vulnerability aligns with CWE-134, which describes the weakness of using externally-influenced format strings, a category that encompasses format string vulnerabilities in software applications. This weakness is particularly dangerous in web server environments where user input is frequently processed and rendered in various contexts. The attack vectors identified in CVE-2016-4864 correspond to common threat patterns found in the MITRE ATT&CK framework under the T1499 category of Network Denial of Service, where adversaries target network services to make them unavailable to legitimate users. Organizations should prioritize immediate patching of affected systems to prevent exploitation, as the vulnerability does not require special privileges or authentication to exploit. The recommended mitigation strategy involves upgrading to H2O versions that have addressed this vulnerability through proper input validation and format string handling mechanisms. Additionally, implementing network segmentation, monitoring for unusual traffic patterns, and deploying intrusion detection systems can help detect and prevent exploitation attempts while awaiting patch deployment.