Two vunerabilities were discovered in c-ares, an asynchronous name
ares_inet_net_pton() is found to be 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, however external usage for other purposes may
cause more severe issues.
Target resolver may erroneously interprets a malformed UDP packet
with a lenght of 0 as a graceful shutdown of the connection, which
could cause a denial of service.
For the stable distribution (bullseye), these problems have been fixed in version 1.17.1-1+deb11u3.
We recommend that you upgrade your c-ares packages.