CVE-2018-16470 in Rack
Summary
by MITRE
There is a possible DoS vulnerability in the multipart parser in Rack before 2.0.6. Specially crafted requests can cause the multipart parser to enter a pathological state, causing the parser to use CPU resources disproportionate to the request size.
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Analysis
by VulDB Data Team • 06/06/2023
The vulnerability identified as CVE-2018-16470 represents a critical denial of service weakness within the Rack web application framework's multipart parser component. This issue affects versions prior to 2.0.6 and stems from inadequate handling of specially crafted HTTP requests that exploit the parser's state management mechanisms. The vulnerability operates at the application layer and specifically targets the processing of multipart form data commonly used in web applications for file uploads and complex data submissions.
The technical flaw manifests when maliciously constructed requests are processed by the multipart parser, causing it to enter a pathological state where CPU consumption grows exponentially relative to the input size. This occurs due to insufficient bounds checking and state validation within the parser's internal algorithms, allowing attackers to craft requests that trigger inefficient processing loops or recursive operations. The vulnerability is classified under CWE-400 as an uncontrolled resource consumption issue, where the system's resources are consumed in a manner that exceeds normal operational parameters. The parser's failure to properly validate input structure and limit processing iterations creates an environment where malicious actors can exploit the framework's handling of multipart data.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged to exhaust server resources and potentially cause cascading failures in web applications. Attackers can construct relatively small requests that trigger massive CPU usage, making this a particularly effective vector for resource exhaustion attacks. Applications utilizing affected Rack versions become vulnerable to both direct denial of service attempts and indirect attacks that exploit the framework's resource consumption patterns. The vulnerability can be exploited through standard HTTP POST requests containing malformed multipart data, making it accessible to attackers with minimal specialized tools or knowledge. This weakness directly aligns with ATT&CK technique T1499.004, which describes resource exhaustion attacks targeting application availability.
Mitigation strategies for CVE-2018-16470 focus primarily on upgrading to Rack version 2.0.6 or later, which includes enhanced bounds checking and improved state management within the multipart parser. Organizations should also implement request size limits and rate limiting mechanisms at their application firewalls or load balancers to prevent excessive resource consumption. Additional protective measures include configuring application-level input validation to reject malformed multipart data and monitoring for unusual CPU consumption patterns that may indicate exploitation attempts. Security teams should conduct comprehensive testing to ensure that the upgrade does not introduce compatibility issues with existing application functionality while maintaining proper resource allocation policies to prevent similar vulnerabilities from emerging in other components of the web stack.