https://joshua.hu/cjson-json-parser-cve-vulnerabilities says:
cJSON is probably the most widely used JSON parser in the C world. It’s vendored into ESP-IDF, into a lot of embedded firmware, and into a whole lot more server-side C. I found 33 security issues in it, using a mix of AI and some manual fuzzing and review. They affect every version up to and including v1.7.19, and every one of them is still in the current code.Looking at cJSON’s GitHub, several of these issues have been reported before, some with working proofs of concept attached, and a few of those reports are years old by now. Development has been more or less stagnant for four years. Memory-safety reports sit open and unanswered, and in a few cases the patch that would fix them is sitting right there in the same thread, unmerged. For most of what follows there is simply nothing available to apply. So this is a writeup instead of another bug report. If you ship cJSON, you need to know what’s in it, because nobody is going to hand you a fixed version. Every proof of concept below is complete and self-contained. I compiled them all with: cc -fsanitize=address,undefined -fno-omit-frame-pointer -g -O0 \ -I. cJSON.c cJSON_Utils.c poc.c -o poc -lm One thing to know before you try to reproduce any of this. A few of them only crash with AddressSanitizer and UndefinedBehaviorSanitizer enabled together, on an unoptimised build, because it’s the instrumentation that fattens the stack frames enough to run off the end. With ASan alone, or at -O2, some of them quietly return NULL instead. Test with a partial sanitizer set and this library looks considerably healthier than it is. The first thirteen are memory-safety issues and a denial of service. The rest are logic bugs, most of which lose data or operate on the wrong object member without saying so. In a library whose whole job is applying somebody else’s patch document to your data, I count those. Note: I used AI to help write this post, mostly because there are so many of them and doing 33 of these by hand is miserable. I have no emotional attachment to this project or to these findings, and getting them published seemed more useful than getting the prose exactly the way I’d write it myself. If cJSON is parsing attacker-controlled JSON anywhere in your stack, look at what it would take to move off it. And don’t just merge the unlanded patches sitting on the GitHub repository and call it done, either. Some of those introduce fresh bugs of their own, from what I saw.
See https://joshua.hu/cjson-json-parser-cve-vulnerabilities for the writeups of each claimed vulnerability. CVE-2026-67215, CVE-2026-67216, & CVE-2026-67217 cite this URL as references for the assigned CVE's. https://cert.pl/en/posts/2026/07/CVE-2026-16554/ appears to cover an unrelated vulnerability also disclosed this week.
