CVE-2016-4425 in Jansson
Summary
by MITRE
Jansson 2.7 and earlier allows context-dependent attackers to cause a denial of service (deep recursion, stack consumption, and crash) via crafted JSON data.
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Analysis
by VulDB Data Team • 12/04/2025
The vulnerability identified as CVE-2016-4425 affects the Jansson JSON library version 2.7 and earlier, presenting a significant denial of service risk that stems from inadequate input validation mechanisms. This flaw enables attackers to craft malicious JSON data that triggers deep recursion patterns within the library's parsing routines, ultimately leading to excessive stack consumption and system crashes. The vulnerability operates at the intersection of software design flaws and security implications, where the library's inability to properly handle deeply nested JSON structures creates a pathway for exploitation.
The technical implementation of this vulnerability resides in the recursive parsing algorithms employed by Jansson when processing JSON data structures. When the library encounters malformed or specially crafted JSON input containing deeply nested objects or arrays, it follows recursive parsing paths that consume stack memory at an exponential rate. This behavior aligns with CWE-674, which describes "Uncontrolled Recursion" as a weakness where recursive algorithms lack proper termination conditions or stack depth limits. The flaw essentially allows an attacker to craft input that forces the parser to make an excessive number of recursive calls, with each call consuming stack space until the system's stack limit is exceeded.
From an operational impact perspective, this vulnerability poses a substantial risk to applications that rely on Jansson for JSON processing, particularly those handling untrusted input from external sources. The denial of service condition manifests as application crashes, system instability, and potential service interruption for legitimate users. Attackers can exploit this weakness through various vectors including web applications, API endpoints, or any system component that processes JSON data from potentially malicious sources. The vulnerability's context-dependent nature means that exploitation requires specific conditions where the attacker can control the JSON input being processed, making it particularly dangerous in web-facing applications or services that accept user-provided data.
The attack pattern associated with CVE-2016-4425 follows established methodologies described in the MITRE ATT&CK framework under the technique of "Resource Exhaustion" and "Execution Guardrails." The vulnerability can be categorized under the broader category of DoS attacks targeting software libraries, where attackers leverage implementation weaknesses in parsing functions to consume system resources. This type of attack falls under the domain of software supply chain security, as the vulnerability affects a widely-used library that numerous applications depend upon, potentially creating cascading effects across multiple systems. Organizations using vulnerable versions of Jansson should implement immediate mitigations including input validation, stack limit enforcement, and library version updates to prevent exploitation.
The remediation approach for this vulnerability requires updating to Jansson version 2.8 or later, which includes fixes for the recursive parsing behavior and introduces proper stack depth limitations. Additionally, implementing input validation measures such as maximum nesting depth checks and size limitations for JSON data can provide defense-in-depth protection. Security teams should also consider monitoring for suspicious JSON parsing patterns and implementing rate limiting or circuit breaker mechanisms to prevent exploitation attempts. The fix addresses the underlying CWE-674 weakness by introducing proper recursion depth controls and preventing unbounded stack consumption during JSON parsing operations, thereby restoring system stability and preventing the denial of service conditions that could impact service availability.