CVE-2022-31018 in Play Framework
Summary
by MITRE • 06/02/2022
Play Framework is a web framework for Java and Scala. A denial of service vulnerability has been discovered in verions 2.8.3 through 2.8.15 of Play's forms library, in both the Scala and Java APIs. This can occur when using either the `Form#bindFromRequest` method on a JSON request body or the `Form#bind` method directly on a JSON value. If the JSON data being bound to the form contains a deeply-nested JSON object or array, the form binding implementation may consume all available heap space and cause an `OutOfMemoryError`. If executing on the default dispatcher and `akka.jvm-exit-on-fatal-error` is enabled—as it is by default—then this can crash the application process. `Form.bindFromRequest` is vulnerable when using any body parser that produces a type of `AnyContent` or `JsValue` in Scala, or one that can produce a `JsonNode` in Java. This includes Play's default body parser. This vulnerability been patched in version 2.8.16. There is now a global limit on the depth of a JSON object that can be parsed, which can be configured by the user if necessary. As a workaround, applications that do not need to parse a request body of type `application/json` can switch from the default body parser to another body parser that supports only the specific type of body they expect.
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Analysis
by VulDB Data Team • 06/05/2022
The vulnerability identified as CVE-2022-31018 affects the Play Framework's forms library across versions 2.8.3 through 2.8.15, presenting a critical denial of service risk that stems from insufficient input validation during JSON parsing operations. This flaw specifically targets the Form binding mechanisms in both Scala and Java APIs, where the implementation fails to enforce reasonable limits on JSON structure complexity. The vulnerability manifests when applications process JSON request bodies through either the Form#bindFromRequest method or the Form#bind method, particularly when handling deeply nested JSON objects or arrays that can cause excessive memory consumption during the binding process.
The technical implementation of this vulnerability exploits the recursive nature of JSON parsing within Play Framework's form binding system, where the framework attempts to traverse and map deeply nested structures without adequate depth limiting mechanisms. When a maliciously crafted JSON payload contains excessive nesting levels, the form binding process consumes escalating amounts of heap memory until an OutOfMemoryError occurs. This memory exhaustion typically happens because the framework's parsing algorithm recursively processes nested elements without bounds checking, leading to exponential memory growth proportional to the nesting depth of the JSON structure. The default dispatcher configuration in Play Framework, combined with the akka.jvm-exit-on-fatal-error setting enabled by default, ensures that such memory exhaustion events result in complete application process termination rather than graceful error handling.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise application availability and system stability. Attackers can exploit this weakness by submitting carefully crafted JSON payloads designed to create deeply nested structures that trigger memory exhaustion, effectively performing a resource exhaustion attack against the application server. The vulnerability affects applications using Play's default body parser configurations, which handle AnyContent or JsValue types in Scala and JsonNode types in Java, making it particularly widespread across typical Play Framework deployments. The default nature of the affected body parser means that most applications are vulnerable without requiring specific configuration changes or application code modifications, amplifying the potential attack surface significantly.
Security practitioners should note that this vulnerability aligns with CWE-770, which addresses allocation of resources without limits or with inadequate limits, and represents a classic example of insufficient resource management in web application frameworks. The mitigation strategy implemented in version 2.8.16 introduces a global depth limit for JSON parsing that can be configured according to application requirements, addressing the root cause through proper input validation and resource boundary enforcement. Organizations should prioritize upgrading to version 2.8.16 or later to remediate this vulnerability, while also implementing application-level monitoring to detect unusual memory consumption patterns that might indicate exploitation attempts. The workaround of switching to specific body parsers for non-JSON content provides a temporary mitigation path for applications that cannot immediately upgrade, though this approach requires careful code review and configuration management to ensure complete coverage of all potential attack vectors.
The vulnerability demonstrates the importance of implementing defensive programming practices in web frameworks, particularly around parsing and validation of untrusted input data. It highlights the need for frameworks to establish reasonable default limits on recursive data structures and to provide configurable parameters that allow security-conscious administrators to tune these limits according to their specific operational requirements. The fix implemented by the Play Framework team represents a best practice approach to preventing resource exhaustion attacks by establishing clear boundaries on parsing operations, which aligns with security principles outlined in the OWASP Top Ten and various NIST cybersecurity frameworks. Organizations should also consider implementing additional monitoring and alerting mechanisms to detect potential exploitation attempts and establish incident response procedures specifically designed to handle resource exhaustion attacks against web applications.