CVE-2026-16554: Integer Overflow Leading to Heap Buffer Overflow in cJSON

cJSON library is vulnerable to an integer overflow in the printstringptr() function in cJSON.c on 32-bit platforms. The escapecharacters counter, a 32-bit sizet, can wrap around when processing strings containing approximately 858,993,460 or more control characters, causing the output buffer to be allocated based on an underestimated length. When cJSONPrintBuffered() is used with a pre-allocated buffer, the subsequent write loop overflows the heap allocation. An attacker supplying a crafted JSON string to an application using cJSON on a 32-bit platform can cause a heap buffer overflow, potentially leading to remote code execution, information disclosure, or denial of service.

Because project creator contact attempts were unsuccessful, the vulnerability has only been confirmed in version 1.7.19 but may also affect other versions.