Vulnerability in DaveGamble cJSON library

CERT Polska has received a report about vulnerability in DaveGamble cJSON library and participated in coordination of its disclosure.

The vulnerabilityCVE-2026-16554: cJSON library is vulnerable to an integer overflow in theprint_string_ptr()function incJSON.con 32-bit platforms. Theescape_characterscounter, a 32-bitsize_t, 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. WhencJSON_PrintBuffered()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 vendor contact attempts were unsuccessful, the vulnerability has only been confirmed in version 1.7.19 but may also affect other versions.

We thank Michał Majchrowicz and Marcin Wyczechowski from AFINE Team for the responsible vulnerability report.