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Link Following Affecting unbound package, versions <1.9.0-2+deb10u3

0.0
medium

Snyk CVSS

    Attack Complexity Low
    Availability High

    Threat Intelligence

    EPSS 0.05% (14th percentile)
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NVD
5.5 medium
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SUSE
4.4 medium
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Red Hat
4.4 medium

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  • Snyk ID SNYK-DEBIAN10-UNBOUND-1045777
  • published 26 Nov 2020
  • disclosed 7 Dec 2020
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Introduced: 26 Nov 2020

CVE-2020-28935 Open this link in a new tab
CWE-59 Open this link in a new tab

How to fix?

Upgrade Debian:10 unbound to version 1.9.0-2+deb10u3 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream unbound package and not the unbound package as distributed by Debian. See How to fix? for Debian:10 relevant fixed versions and status.

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.