The extractFrom function in Internals/QuotedString.cpp in Arduino JSON before 4.5 allows remote attackers to cause a denial of service (crash) via a JSON string with a \ (backslash) followed by a terminator, as demonstrated by "\\\0", which triggers a buffer overflow and over-read.
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.