CVE-2018-17851 in JsonCpp
Summary
by MITRE
An issue was discovered in JsonCpp 1.8.4. An unhandled exception vulnerability exists in Json::OurReader::readValue() in json_reader.cpp after throwing an instance of "Json::RuntimeError what(): Exceeded stackLimit." Specially crafted JSON requests can cause an unhandled exception resulting in denial of service. An attacker can send malicious JSON to trigger this vulnerability.
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Analysis
by VulDB Data Team • 05/19/2023
The vulnerability identified as CVE-2018-17851 represents a critical denial of service weakness within the JsonCpp library version 1.8.4. This flaw manifests in the Json::OurReader::readValue() function located in the json_reader.cpp file, where the library fails to properly handle a specific exception condition. The vulnerability occurs when the parser encounters JSON input that exceeds the predefined stackLimit parameter, triggering a Json::RuntimeError exception with the message "Exceeded stackLimit." This particular error condition is not gracefully managed by the library's exception handling mechanisms, leading to abrupt program termination and service disruption.
The technical nature of this vulnerability stems from inadequate exception handling within the JSON parsing logic of JsonCpp. When the parser processes malformed or excessively complex JSON structures, it attempts to maintain stack usage within reasonable limits to prevent stack overflow conditions. However, the current implementation fails to catch and properly respond to the RuntimeError exception that occurs when these limits are exceeded. This results in an unhandled exception that propagates up through the call stack, ultimately causing the application to crash or become unresponsive. The vulnerability specifically relates to CWE-476 which addresses null pointer dereference issues, though in this case the issue manifests as unhandled exception rather than pointer dereference. The flaw demonstrates poor error recovery mechanisms that violate fundamental principles of robust software design and fault tolerance.
From an operational impact perspective, this vulnerability creates significant risk for applications that rely on JsonCpp for JSON processing. An attacker can exploit this weakness by crafting specially formatted JSON payloads that deliberately exceed the stack limit, causing the target application to crash or become unresponsive. This makes the vulnerability particularly dangerous in web applications, APIs, and services that accept JSON input from untrusted sources. The denial of service impact can be severe, potentially affecting availability for legitimate users and creating opportunities for attackers to disrupt service operations. The vulnerability affects any system where JsonCpp 1.8.4 is deployed and processing JSON data, making it a widespread concern across numerous applications and platforms that depend on this popular JSON parsing library. The ATT&CK framework categorizes this as a denial of service attack vector under the technique of "Resource Exhaustion" where system resources are manipulated to prevent normal operation.
The mitigation strategy for CVE-2018-17851 involves several approaches that address both immediate remediation and long-term architectural improvements. The most direct solution is to upgrade to a newer version of JsonCpp that contains the fix for this exception handling issue. Version 1.8.5 and later releases incorporate proper exception handling for stack limit violations, preventing the unhandled exception scenario that leads to service disruption. Organizations should also implement input validation and sanitization measures to prevent malicious JSON data from reaching the vulnerable parsing functions. Additionally, deploying application-level protections such as request rate limiting, input size restrictions, and robust error handling can help reduce the attack surface. From a defensive perspective, implementing proper logging and monitoring around JSON parsing operations can help detect exploitation attempts and provide early warning of potential attacks. The vulnerability highlights the importance of comprehensive exception handling in parsing libraries and underscores the need for security-conscious development practices that consider both functional requirements and security implications during the software development lifecycle.