Debian Security Advisory

DLA-2556-1 unbound1.9 -- LTS security update

Date Reported:
12 Feb 2021
Affected Packages:
Security database references:
In the Debian bugtracking system: Bug 977165.
In Mitre's CVE dictionary: CVE-2020-12662, CVE-2020-12663, CVE-2020-28935.
More information:

Several security vulnerabilities have been corrected in unbound, a validating, recursive, caching DNS resolver. Support for the unbound DNS server has been resumed, the sources can be found in the unbound1.9 source package.

  • CVE-2020-12662

    Unbound has Insufficient Control of Network Message Volume, aka an NXNSAttack issue. This is triggered by random subdomains in the NSDNAME in NS records.

  • CVE-2020-12663

    Unbound has an infinite loop via malformed DNS answers received from upstream servers.

  • CVE-2020-28935

    Unbound contains a local vulnerability that would allow for a local symlink attack. When writing the PID file Unbound creates the file if it is not there, or opens an existing file for writing. In case the file was already present, it would follow symlinks if the file happened to be a symlink instead of a regular file.

For Debian 9 stretch, these problems have been fixed in version 1.9.0-2+deb10u2~deb9u1.

We recommend that you upgrade your unbound1.9 packages.

For the detailed security status of unbound1.9 please refer to its security tracker page at:

Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: