Do you have a specific library in mind? I think it would have to be an ancient, unmaintained C library.
But I think most OSS code isn't like this -- even C code born long ago, if it's still in wide use, has been hardened by now. Examples: Linux kernel, GNU userland, PostgreSQL, Python.
> even C code born long ago, if it's still in wide use, has been hardened by now. Examples: Linux kernel
There have been two LPE vulnerability and exploits in the Linux kernel announced today. After the one announced just last week. I don't think as much of the C code born long ago has been as carefully hardened as you think.
(Copy Fail 2 and Dirty Frag today, and Copy Fail last week)