Link following in Unbound - CVE-2020-28935

CSH
CYBERSECURITY HELP
Sign In REGISTER
 
Main Vulnerability Database Vulnerabilities #VU48897

Link following in Unbound - CVE-2020-28935

Published: December 7, 2020 / Updated: December 9, 2020


Vulnerability identifier: #VU48897
CSH Severity: Low
CVSS v4: 6.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2020-28935
CWE-ID: CWE-59
Exploitation vector: Local access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a local authenticated user to perform a denial of service (DoS) attack.

NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs NSD, up to and including version 4.3.3, contain a local vulnerability that would allow for a local symlink attack. When writing the PID file, Unbound and NSD create the file if it is not there, or open an existing file for writing. In case the file was already present, they would follow symlinks if the file happened to be a symlink instead of a regular file. An additional chown of the file would then take place after it was written, making the user Unbound/NSD is supposed to run as the new owner of the file. If an attacker has local access to the user Unbound/NSD runs as, she could create a symlink in place of the PID file pointing to a file that she would like to erase. If then Unbound/NSD is killed and the PID file is not cleared, upon restarting with root privileges, Unbound/NSD will rewrite any file pointed at by the symlink. This is a local vulnerability that could create a Denial of Service of the system Unbound/NSD is running on. It requires an attacker having access to the limited permission user Unbound/NSD runs as and point through the symlink to a critical file on the system.


Affected software

Unbound
Arch Linux
Gentoo Linux
SUSE CaaS Platform
SUSE Manager Proxy
SUSE Manager Retail Branch Server
SUSE Manager Server
SUSE Enterprise Storage
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for ARM 64
Red Hat Enterprise Linux Server - TUS
SUSE Linux Enterprise High Performance Computing
SUSE Linux Enterprise Server
SUSE Linux Enterprise Server for SAP
SUSE Linux Enterprise Realtime Extension
SUSE Linux Enterprise Module for Basesystem
Ubuntu
openEuler
cflinuxfs3
unbound (Red Hat package)
nsd (Alpine package)
unbound (Ubuntu package)
libunbound2 (Ubuntu package)
libunbound2-debuginfo
libunbound2
unbound-anchor
unbound-anchor-debuginfo
unbound-debuginfo
unbound-debugsource
unbound-devel
libunbound8 (Ubuntu package)
python3-unbound
unbound-help
unbound-libs
unbound
OpenShift Virtualization

How to mitigate CVE-2020-28935

Install update from vendor's website.

Unbound - update to 1.13.0
cflinuxfs3 - update to 0.237.0
unbound (Red Hat package) - addressed in versions 1.7.3-12.el8_2, 1.7.3-15.el8
nsd (Alpine package) - update to 4.3.4-r0
unbound (Ubuntu package) - addressed in versions 1.6.7-1ubuntu2.4, 1.9.4-2ubuntu1.2
libunbound2 (Ubuntu package) - update to 1.6.7-1ubuntu2.4
libunbound2-debuginfo - addressed in versions 1.6.8-3.9.1, 1.6.8-10.6.1
libunbound2 - addressed in versions 1.6.8-3.9.1, 1.6.8-10.6.1
unbound-anchor - addressed in versions 1.6.8-3.9.1, 1.6.8-10.6.1
unbound-anchor-debuginfo - addressed in versions 1.6.8-3.9.1, 1.6.8-10.6.1
unbound-debuginfo - addressed in versions 1.6.8-3.9.1, 1.6.8-10.6.1
unbound-debugsource - addressed in versions 1.6.8-3.9.1, 1.6.8-10.6.1
unbound-devel - addressed in versions 1.6.8-3.9.1, 1.6.8-10.6.1
libunbound8 (Ubuntu package) - update to 1.9.4-2ubuntu1.2
unbound-devel - update to 1.11.0-2
unbound-debugsource - update to 1.11.0-2
python3-unbound - update to 1.11.0-2
unbound-debuginfo - update to 1.11.0-2
unbound-help - update to 1.11.0-2
unbound-libs - update to 1.11.0-2
unbound - update to 1.11.0-2
OpenShift Virtualization - addressed in versions 2.6.6, 4.8.0

External References

Related Security Bulletins