CVE-2016-6622 in phpMyAdmin
Summary
by MITRE
An issue was discovered in phpMyAdmin. An unauthenticated user is able to execute a denial-of-service (DoS) attack by forcing persistent connections when phpMyAdmin is running with $cfg['AllowArbitraryServer']=true. All 4.6.x versions (prior to 4.6.4), 4.4.x versions (prior to 4.4.15.8), and 4.0.x versions (prior to 4.0.10.17) are affected.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-6622 represents a critical denial-of-service weakness in phpMyAdmin that exploits the application's configuration settings to disrupt service availability. This flaw specifically targets installations where the AllowArbitraryServer configuration parameter is enabled, creating a condition where unauthenticated attackers can systematically consume system resources and render the application unavailable to legitimate users. The vulnerability affects multiple version lines including 4.0.x, 4.4.x, and 4.6.x, with specific patch versions provided for each affected series. The issue stems from phpMyAdmin's handling of persistent connections when arbitrary server connections are permitted, creating a resource exhaustion scenario that can be easily exploited without requiring authentication credentials.
The technical mechanism behind this vulnerability involves the exploitation of phpMyAdmin's connection management system when operating under the AllowArbitraryServer setting. When this configuration is enabled, the application permits users to connect to arbitrary MySQL servers through the web interface, but fails to properly limit or manage persistent connection requests. An attacker can repeatedly establish persistent connections to target servers, causing phpMyAdmin to consume increasing amounts of memory and system resources. This behavior aligns with CWE-400, which classifies unchecked resource consumption as a fundamental weakness in resource management. The vulnerability operates at the application layer and can be classified under the ATT&CK technique T1499.004 for Network Denial of Service, where attackers leverage application-specific weaknesses to exhaust system resources.
The operational impact of CVE-2016-6622 extends beyond simple service disruption to potentially compromise entire database server availability and system stability. Organizations running affected phpMyAdmin versions with AllowArbitraryServer enabled face significant risk of unauthorized service disruption, particularly in environments where database administrators might enable this feature for legitimate remote management purposes. The vulnerability can be exploited by any internet-connected attacker without requiring prior authentication, making it particularly dangerous for publicly accessible phpMyAdmin installations. The resource exhaustion effect can lead to system crashes, memory exhaustion, and performance degradation that affects not only the phpMyAdmin interface but also the underlying database servers that the application manages. This vulnerability particularly impacts web hosting environments, managed database services, and organizations with exposed phpMyAdmin interfaces where the configuration might be inadvertently left enabled for convenience.
Mitigation strategies for CVE-2016-6622 focus primarily on immediate version upgrades to patched releases and configuration hardening. Organizations should immediately upgrade to phpMyAdmin versions 4.0.10.17, 4.4.15.8, or 4.6.4, which contain the necessary code fixes for the persistent connection handling issue. Additionally, administrators should disable the AllowArbitraryServer configuration setting in phpMyAdmin when it is not strictly required for administrative tasks, as this parameter fundamentally enables the vulnerability. Network-level protections such as firewall rules and access control lists can help limit exposure by restricting access to phpMyAdmin interfaces to trusted IP ranges. The implementation of connection rate limiting and resource monitoring can provide additional defense-in-depth measures to detect and prevent exploitation attempts. Security teams should also conduct comprehensive audits of phpMyAdmin configurations across their infrastructure to identify and remediate any instances where arbitrary server connections are enabled unnecessarily, as this represents a common misconfiguration that can lead to various security issues beyond just denial-of-service attacks.