CVE-2019-14439 in jackson-databind
Summary
by MITRE
A Polymorphic Typing issue was discovered in FasterXML jackson-databind 2.x before 2.9.9.2. This occurs when Default Typing is enabled (either globally or for a specific property) for an externally exposed JSON endpoint and the service has the logback jar in the classpath.
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Analysis
by VulDB Data Team • 11/14/2023
The vulnerability CVE-2019-14439 represents a critical polymorphic typing flaw within the FasterXML jackson-databind library, specifically affecting versions prior to 2.9.9.2. This issue manifests when default typing is enabled for externally accessible JSON endpoints and the application classpath includes the logback jar library. The vulnerability stems from the dangerous combination of automatic type handling and the presence of certain logging components that can be exploited by malicious actors to execute arbitrary code on affected systems. The flaw essentially allows attackers to manipulate the deserialization process and inject malicious payloads through carefully crafted JSON input.
The technical root cause of this vulnerability lies in how jackson-databind handles polymorphic typing when default typing is enabled. When Default Typing is activated, the library automatically includes type information in the serialized output, which can then be used during deserialization to instantiate objects of specific types. The presence of logback in the classpath creates additional attack surface by providing classes that can be leveraged for code execution. This vulnerability is particularly dangerous because it can be exploited through JSON endpoints that are exposed to untrusted input, making it a prime target for remote code execution attacks. The flaw operates at the deserialization layer where input validation is insufficient, allowing attackers to bypass normal security boundaries.
The operational impact of CVE-2019-14439 is severe and far-reaching across numerous applications that utilize jackson-databind for JSON processing. Systems running affected versions become vulnerable to remote code execution attacks that can result in complete system compromise, data exfiltration, and persistent backdoor access. The vulnerability affects any application that exposes JSON endpoints to external users and uses jackson-databind with default typing enabled. Organizations using web applications, APIs, or microservices that process external JSON input are at risk, particularly those with logback logging configurations. The attack vector is straightforward - an attacker sends maliciously crafted JSON data containing type information that triggers the vulnerable deserialization path, leading to arbitrary code execution on the target system.
Mitigation strategies for CVE-2019-14439 focus primarily on upgrading to jackson-databind version 2.9.9.2 or later, which contains the necessary patches to address the polymorphic typing issue. Organizations should also implement strict input validation and avoid enabling default typing for external endpoints unless absolutely necessary. The recommended approach includes disabling default typing globally or for specific properties when it's not required, and implementing proper type whitelisting mechanisms to restrict which classes can be instantiated during deserialization. Security teams should also consider implementing network-level protections such as firewalls and intrusion detection systems to monitor for suspicious JSON traffic patterns. Additionally, following the principle of least privilege and implementing application sandboxing can help limit the potential damage if an exploit is successfully executed. This vulnerability aligns with CWE-502, which addresses deserialization of untrusted data, and maps to ATT&CK technique T1203, focusing on exploitation of remote services through deserialization vulnerabilities.
The vulnerability demonstrates the critical importance of secure deserialization practices in modern application development and highlights the risks associated with automatic type handling in JSON processing libraries. Organizations should conduct comprehensive vulnerability assessments to identify all instances of affected jackson-databind versions and ensure proper patch management procedures are in place. Regular security testing including static analysis and dynamic application security testing should be implemented to detect similar vulnerabilities in custom code and third-party libraries. The incident underscores the necessity of maintaining up-to-date security practices and the importance of understanding the full attack surface when integrating third-party components into applications.