CVE-2016-9589 in WildFly
Summary
by MITRE
Undertow in Red Hat wildfly before version 11.0.0.Beta1 is vulnerable to a resource exhaustion resulting in a denial of service. Undertow keeps a cache of seen HTTP headers in persistent connections. It was found that this cache can easily exploited to fill memory with garbage, up to "max-headers" (default 200) * "max-header-size" (default 1MB) per active TCP connection.
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Analysis
by VulDB Data Team • 02/21/2023
The vulnerability identified as CVE-2016-9589 affects the Undertow web server component within Red Hat WildFly application server versions prior to 11.0.0.Beta1. This represents a critical resource exhaustion flaw that can be exploited to cause denial of service conditions. The vulnerability stems from how Undertow handles HTTP header caching during persistent connections, creating a pathway for malicious actors to consume excessive system resources. The flaw operates by leveraging the HTTP header cache mechanism that is designed to optimize performance through header reuse, but becomes a liability when improperly controlled. This vulnerability directly impacts the availability and stability of web applications running on affected WildFly versions, potentially disrupting business operations and service delivery.
The technical implementation of this vulnerability resides in Undertow's header caching mechanism that maintains a cache of previously seen HTTP headers to improve performance during persistent connections. By default, Undertow maintains a maximum of 200 headers per connection with each header potentially reaching 1MB in size, creating a theoretical maximum memory consumption of 200MB per active TCP connection. Attackers can exploit this by sending HTTP requests with a large number of unique headers that exceed the configured limits, causing the cache to fill with garbage data that cannot be effectively garbage collected. The flaw allows for rapid memory exhaustion through repeated connections, with each connection consuming significant amounts of heap memory. This behavior aligns with CWE-400, which addresses uncontrolled resource consumption, and demonstrates how seemingly benign caching mechanisms can become attack vectors when not properly bounded.
The operational impact of CVE-2016-9589 extends beyond simple denial of service to potentially compromise entire application server instances. When exploited successfully, the vulnerability can cause the application server to consume all available memory, leading to process crashes, system instability, and complete service unavailability. The attack can be executed with relatively simple HTTP requests, making it accessible to attackers with minimal technical expertise. The vulnerability affects all applications running on affected WildFly versions, regardless of their specific configuration or security posture. This makes it particularly dangerous in production environments where multiple applications may be simultaneously vulnerable. The memory exhaustion occurs gradually but predictably, allowing attackers to systematically consume resources until the system becomes unresponsive. The impact is exacerbated by the fact that these connections can remain active for extended periods, prolonging the resource consumption and making detection more difficult.
Organizations should immediately upgrade to Red Hat WildFly version 11.0.0.Beta1 or later to remediate this vulnerability, as no effective workarounds exist for the underlying caching mechanism. System administrators should monitor for unusual memory consumption patterns and implement connection rate limiting to reduce the attack surface. The vulnerability demonstrates the importance of proper resource bounds checking and memory management in web server components. Security teams should also consider implementing network-level controls to limit the number of headers allowed in HTTP requests and monitor for unusual header patterns that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network denial of service, and T1566.001, which addresses spearphishing through social engineering. The vulnerability underscores the need for comprehensive security testing of web server components and proper configuration management to prevent resource exhaustion attacks that can compromise system availability and business continuity.