CVE-2016-4303 in cJSON Library
Summary
by MITRE
The parse_string function in cjson.c in the cJSON library mishandles UTF8/16 strings, which allows remote attackers to cause a denial of service (crash) or execute arbitrary code via a non-hex character in a JSON string, which triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 01/15/2025
The CVE-2016-4303 vulnerability resides within the cJSON library's parse_string function in cjson.c, representing a critical security flaw that affects applications relying on this lightweight JSON parsing library. This vulnerability specifically targets the handling of UTF8 and UTF16 string encodings, creating a pathway for remote attackers to exploit malformed JSON data. The flaw manifests when the library encounters non-hex characters within JSON strings, triggering a heap-based buffer overflow condition that can result in system instability or complete compromise.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the cJSON parsing routine. When processing JSON strings containing UTF8/16 encoded data, the parse_string function fails to properly validate character sequences, particularly non-hex characters that should be handled as part of valid Unicode escape sequences. This improper handling creates a condition where the library attempts to write data beyond the allocated buffer boundaries, leading to memory corruption. The heap-based nature of the overflow means that attackers can manipulate memory layout to achieve arbitrary code execution, making this vulnerability particularly dangerous in server environments where cJSON is used to process untrusted JSON input from network sources.
The operational impact of CVE-2016-4303 extends beyond simple denial of service scenarios, as the vulnerability can be exploited to execute arbitrary code on affected systems. This makes it a prime target for attackers seeking to gain unauthorized access to systems processing JSON data, particularly in web applications, API endpoints, and network services that utilize the cJSON library. The vulnerability affects a wide range of applications including web servers, mobile applications, and embedded systems that depend on cJSON for JSON parsing operations. Systems running vulnerable versions of cJSON are at risk of complete compromise, as the heap overflow can be leveraged to overwrite critical program memory structures or inject malicious code into the executing process.
Mitigation strategies for CVE-2016-4303 require immediate patching of affected cJSON library versions, with the implementation of proper input validation and bounds checking mechanisms. Organizations should prioritize updating to patched versions of the cJSON library while implementing additional security controls such as input sanitization and network segmentation to limit potential attack surface. The vulnerability aligns with CWE-121, heap-based buffer overflow, and maps to attack patterns in the ATT&CK framework under execution techniques involving code injection and privilege escalation. Security teams should also consider implementing runtime monitoring and intrusion detection systems to identify potential exploitation attempts targeting this vulnerability in their environments.