CVE-2011-0534 in Tomcat
Summary
by MITRE
Apache Tomcat 7.0.0 through 7.0.6 and 6.0.0 through 6.0.30 does not enforce the maxHttpHeaderSize limit for requests involving the NIO HTTP connector, which allows remote attackers to cause a denial of service (OutOfMemoryError) via a crafted request.
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Analysis
by VulDB Data Team • 12/28/2024
Apache Tomcat versions 7.0.0 through 7.0.6 and 6.0.0 through 6.0.30 contain a critical denial of service vulnerability in the NIO HTTP connector implementation that fails to properly enforce the maxHttpHeaderSize configuration limit. This vulnerability arises from the improper handling of HTTP header size constraints within the non-blocking I/O connector mechanism, creating a pathway for remote attackers to exploit memory allocation behaviors. The flaw specifically affects the NIO connector variant which is designed for high-performance HTTP handling through asynchronous I/O operations. When a maliciously crafted HTTP request is processed through this connector, the system allocates memory based on the request header size without properly validating against the configured maxHttpHeaderSize parameter, leading to excessive memory consumption and eventual OutOfMemoryError conditions.
The technical implementation of this vulnerability stems from the NIO connector's failure to validate HTTP header sizes against the configured limits during request processing. In standard Tomcat operation, administrators can configure the maxHttpHeaderSize parameter to limit the maximum size of HTTP headers that the server will accept, typically set to prevent memory exhaustion attacks. However, the NIO connector bypasses this validation mechanism, allowing requests with oversized headers to proceed without size restriction enforcement. This behavior creates a memory exhaustion scenario where the JVM heap becomes saturated with header data, ultimately triggering OutOfMemoryError conditions that cause the Tomcat server to become unresponsive and require manual intervention for recovery. The vulnerability is particularly dangerous because it operates at the HTTP protocol level and can be exploited through simple network requests without requiring authentication or privileged access.
The operational impact of this vulnerability extends beyond simple denial of service conditions to include potential system instability and service disruption across enterprise environments. Organizations running affected Tomcat versions in production environments face significant risk of service interruptions when malicious actors exploit this vulnerability through carefully crafted HTTP requests containing oversized headers. The memory exhaustion resulting from this vulnerability can cause cascading failures throughout the application stack, potentially affecting multiple services or applications hosted on the same server instance. Network administrators and security teams must consider the broader implications of this vulnerability, as it can be exploited in automated attack scenarios where multiple requests are sent in rapid succession to maximize memory consumption. The vulnerability also affects the availability of legitimate services since the system resources consumed by malicious requests can prevent normal operations from functioning correctly.
Mitigation strategies for this vulnerability require immediate patching of affected Tomcat versions to the latest available releases that contain the fix for the NIO connector header size validation. Organizations should also implement network-level controls such as rate limiting and header size monitoring to detect and prevent exploitation attempts. The recommended approach includes upgrading to Tomcat versions 7.0.7 or later and 6.0.31 or later where the fix has been implemented. Additionally, administrators should review and properly configure the maxHttpHeaderSize parameter in their server.xml configuration files to ensure that reasonable limits are enforced across all HTTP connector configurations. Security teams should also consider implementing intrusion detection systems that can monitor for unusual HTTP header patterns and excessive memory consumption behaviors. This vulnerability aligns with CWE-122 (Heap Overflow) and CWE-400 (Uncontrolled Resource Consumption) categories, and represents a significant concern for ATT&CK technique T1499.004 (Endpoint Denial of Service) as it specifically targets resource exhaustion at the application layer. Organizations should also conduct thorough testing of patched environments to ensure that legitimate application functionality remains intact while the vulnerability is addressed.