Several security vulnerabilities have been discovered in unbound, a validating, recursive, caching DNS resolver.
Unbound is vulnerable to a novel type of the ghost domain names attack. The vulnerability works by targeting an Unbound instance. Unbound is queried for a rogue domain name when the cached delegation information is about to expire. The rogue nameserver delays the response so that the cached delegation information is expired. Upon receiving the delayed answer containing the delegation information, Unbound overwrites the now expired entries. This action can be repeated when the delegation information is about to expire making the rogue delegation information ever-updating. From now on Unbound stores the start time for a query and uses that to decide if the cached delegation information can be overwritten. * CVE-2020-28935 Unbound contains a local vulnerability that would allow for a local symlink attack.
For Debian 10 buster, these problems have been fixed in version 1.9.0-2+deb10u3.
We recommend that you upgrade your unbound packages.
For the detailed security status of unbound please refer to its security tracker page at: https://security-tracker.debian.org/tracker/unbound
Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: https://wiki.debian.org/LTS