c-ares is an asynchronous resolver library. aresinetnetpton() is vulnerable to a buffer underflow for certain ipv6 addresses, in particular "0::00:00:00/2" was found to cause an issue. C-ares only uses this function internally for configuration purposes which would require an administrator to configure such an address via aressetsortlist(). However, users may externally use aresinetnetpton() for other purposes and thus be vulnerable to more severe issues. This issue has been fixed in 1.19.1.