Florian Maury from ANSSI discovered that unbound, a validating, recursive, and caching DNS resolver, was prone to a denial of service vulnerability. An attacker crafting a malicious zone and able to emit (or make emit) queries to the server can trick the resolver into following an endless series of delegations, leading to resource exhaustion and huge network usage.
For the stable distribution (wheezy), this problem has been fixed in version 1.4.17-3+deb7u2.
For the upcoming stable distribution (jessie), this problem has been fixed in version 1.4.22-3.
For the unstable distribution (sid), this problem has been fixed in version 1.4.22-3.
We recommend that you upgrade your unbound packages.