Hello! During exploring mongo r8.0.9 I found some fuzzing tests in master branch. Fromjson fuzzer is one of them, which I backported to version r8.0.9. ASAN detected error in 3rd party library code (Intel RDF Math Library). Its'not part of MongoDB, but how about to add some fixes? 

ASAN error description:

When parsing a JSON document containing a $numberDecimal field with a numeric literal longer than 100 characters, the fromjson function initiates a call chain leading to __bid128_from_string in the third-party Intel RDF Math Library (bid128_string.c). In this function, a buffer char buffer[100] is allocated on the stack (line 295), but when processing a long number, the loop on line 632 accesses this buffer at an index greater than 99 (buffer[i] > '0'), resulting in a stack-buffer-overflow. This crash is reproducible on a 308-byte test case and can be used by an attacker to perform a denial of service (DoS). The expected behavior is correct error handling or rejection of an overly long number without crashing the server. The issue was discovered using fuzzing (libfuzzer + ASAN) and requires a fix in the Decimal128 parsing code.

I explored this part of 3rd party code in mongodb master branch and found that error is actual for latest version too. If you interesting in patching, I can open pr with possible fix