CVE-2012-2733 in Tomcat
Summary
by MITRE
java/org/apache/coyote/http11/InternalNioInputBuffer.java in the HTTP NIO connector in Apache Tomcat 6.x before 6.0.36 and 7.x before 7.0.28 does not properly restrict the request-header size, which allows remote attackers to cause a denial of service (memory consumption) via a large amount of header data.
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Analysis
by VulDB Data Team • 12/20/2021
The vulnerability identified as CVE-2012-2733 represents a critical denial of service flaw within Apache Tomcat's HTTP NIO connector implementation. This weakness exists in the InternalNioInputBuffer.java component that handles HTTP request processing for the NIO (Non-blocking I/O) connector mechanism. The vulnerability specifically affects Apache Tomcat versions 6.x prior to 6.0.36 and 7.x prior to 7.0.28, making it a long-standing issue that impacted numerous production environments. The flaw stems from inadequate validation of request-header size limitations, creating a pathway for malicious actors to exploit memory consumption patterns within the application server.
The technical nature of this vulnerability resides in the improper restriction of request-header size within the NIO connector's input buffer management. When processing HTTP requests, the affected Tomcat versions fail to enforce adequate limits on the amount of header data that can be transmitted in a single request. This allows attackers to craft HTTP requests containing exceptionally large header sections that exceed normal operational parameters. The InternalNioInputBuffer component processes these requests without sufficient size validation, leading to uncontrolled memory allocation as the server attempts to accommodate increasingly large header data structures.
From an operational impact perspective, this vulnerability creates a severe denial of service condition that can effectively compromise the availability of web applications hosted on affected Tomcat instances. Attackers can consume system memory resources at an accelerating rate by sending requests with oversized headers, potentially leading to application server crashes, memory exhaustion, or complete system unresponsiveness. The memory consumption pattern typically follows a predictable trajectory where each malicious request consumes additional memory, eventually depleting available resources and rendering the service unavailable to legitimate users. This makes the vulnerability particularly dangerous in high-traffic environments where multiple concurrent attacks can quickly overwhelm system resources.
The vulnerability aligns with CWE-400, which catalogs weaknesses related to resource exhaustion, and demonstrates characteristics consistent with attack patterns found in the MITRE ATT&CK framework under the service stoppage and resource exhaustion tactics. Organizations running vulnerable Tomcat versions face significant risk of operational disruption, particularly in environments where automated attack tools can systematically exploit this weakness. The attack vector requires only basic HTTP request crafting capabilities, making it accessible to threat actors with minimal technical expertise. Security teams must implement immediate mitigation strategies including version upgrades to patched releases, implementation of request size limits through configuration parameters, and network-level restrictions to prevent malicious header data from reaching vulnerable systems.
The remediation approach centers on upgrading to patched versions of Apache Tomcat where the vulnerability has been addressed through enhanced header size validation mechanisms. Additionally, administrators should configure appropriate request size limits within the Tomcat connector configuration to prevent excessive header processing. Network-level controls including firewalls and load balancers can provide additional defense-in-depth by filtering requests with suspicious header characteristics. Regular security assessments and monitoring of system resource consumption patterns help detect potential exploitation attempts and ensure continued protection against similar vulnerabilities in the Tomcat ecosystem.