unbound: CVE-2020-28935

Debian Bug report logs - #977165
unbound: CVE-2020-28935

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Message #5 received at submit@bugs.debian.org (full text, mbox, reply):

From: Salvatore Bonaccorso <carnil@debian.org>

To: Debian Bug Tracking System <submit@bugs.debian.org>

Subject: unbound: CVE-2020-28935

Date: Fri, 11 Dec 2020 23:41:42 +0100

Source: unbound
Version: 1.12.0-1
Severity: important
Tags: security upstream
Forwarded: https://github.com/NLnetLabs/unbound/issues/303
X-Debbugs-Cc: carnil@debian.org, Debian Security Team <team@security.debian.org>

Hi,

The following vulnerability was published for unbound.

CVE-2020-28935[0]:
| 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.


If you fix the vulnerability please also make sure to include the
CVE (Common Vulnerabilities & Exposures) id in your changelog entry.

For further information see:

[0] https://security-tracker.debian.org/tracker/CVE-2020-28935
    https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-28935
[1] https://github.com/NLnetLabs/unbound/issues/303
[2] https://github.com/NLnetLabs/unbound/commit/ad387832979b6ce4c93f64fe706301cd7d034e87

Please adjust the affected versions in the BTS as needed.

Regards,
Salvatore

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