REDHAT-BUG-2520655: Buffer Overflow

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has an off-by-one stack buffer overflow in evdns.c when dnsnametolabels formats a name-bearing DNS record at the end of the 64 KB stack buffer allocated by evdnsserverrequestformatresponse. The final-label check permits j plus labellen plus one to equal buflen, after which the terminating null byte is written to buf[buflen]. A crafted DNS server response containing PTR, CNAME, MX, NS, or SOA data can trigger the one-byte out-of-bounds write and crash or corrupt the process. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.