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CVE-2020-28935

20
FAUCET Score

CVE-2020-28935 describes a local symlink vulnerability in NLnet Labs Unbound (up to 1.12.0) and NSD (up to 4.3.3). An attacker with local access to the user Unbound/NSD runs as could create a symlink in place of the PID file, allowing the service to overwrite an arbitrary file upon restart with root privileges. This vulnerability has a CVSS score of 5.5 (Medium), indicating a local attack vector with low complexity, low privileges required, and a high impact on availability (Denial of Service). There is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage for this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 4.3.4CPE matchmatch criteria
cpe:2.3:a:nlnetlabs:name_server_daemon:*:*:*:*:*:*:*:*
< 1.13.0CPE matchmatch criteria
cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*
9.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.5MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
1.8
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.48%
Probability of exploitation in next 30 days
EPSS Percentile
39.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0048 is in the 92nd percentile among its peer group of 15,940 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.0 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (4)

microsoftpatch availablevia msrc
Product: 19148-16820Fixed in: 1.10.0-4
microsoftpatch availablevia msrc
Product: 19149-16823Fixed in: 1.10.0-5
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: unbound-0:1.7.3-15.el8
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.2 Extended Update SupportFixed in: unbound-0:1.7.3-12.el8_2
View patch

Vendor Advisories (2)

microsoft2020-Dec/CVE-2020-28935Moderate

Local symlink attack in Unbound and NSD

Dec 8, 2020
redhatCVE-2020-28935Low

unbound: symbolic link traversal when writing PID file

Sep 9, 2020

References

lists.debian.org / debian-lts-announce/2021/02/msg00017.html
Mailing ListThird Party Advisory
lists.debian.org / debian-lts-announce/2023/03/msg00024.html
security.gentoo.org / glsa/202101-38
Third Party Advisory
nlnetlabs.nl / downloads/nsd/CVE-2020-28935.txt
Vendor Advisory
nlnetlabs.nl / downloads/unbound/CVE-2020-28935.txt
Vendor Advisory