Debian DLA-2556-1 : unbound1.9 security update

high Nessus Plugin ID 146527


The remote Debian host is missing a security update.


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.


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


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


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:

NOTE: Tenable Network Security has extracted the preceding description block directly from the DLA security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.


Upgrade the affected packages.

See Also

Plugin Details

Severity: High

ID: 146527

File Name: debian_DLA-2556.nasl

Version: 1.3

Type: local

Agent: unix

Published: 2/16/2021

Updated: 1/22/2024

Supported Sensors: Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Nessus

Risk Information


Risk Factor: Low

Score: 3.6


Risk Factor: Medium

Base Score: 5

Temporal Score: 3.7

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS Score Source: CVE-2020-12663


Risk Factor: High

Base Score: 7.5

Temporal Score: 6.5

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: p-cpe:/a:debian:debian_linux:libunbound8, p-cpe:/a:debian:debian_linux:unbound, p-cpe:/a:debian:debian_linux:unbound-anchor, p-cpe:/a:debian:debian_linux:unbound-host, cpe:/o:debian:debian_linux:9.0

Required KB Items: Host/local_checks_enabled, Host/Debian/release, Host/Debian/dpkg-l

Exploit Ease: No known exploits are available

Patch Publication Date: 2/12/2021

Vulnerability Publication Date: 5/19/2020

Reference Information

CVE: CVE-2020-12662, CVE-2020-12663, CVE-2020-28935