CVE-2020-8621 | Attempting QNAME minimization after forwarding can lead to an assertion failure in resolver.c

In BIND 9.14.0 -> 9.16.5, 9.17.0 -> 9.17.3, If a server is configured with both QNAME minimization and 'forward first' then an attacker who can send queries to it may be able to trigger the condition that will cause the server to crash. Servers that 'forward only' are not affected.

Published: 2020-08-21 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-8621 is rated Moderate Risk (57.9/100): CVSS High severity, with medium exploitation likelihood (EPSS 2.94%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2020-8621

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 4.88% 2.94% -1.93%
2 2026-02-27 4.22% 4.88% +0.66%
3 2025-12-28 — 4.22% —

Full EPSS history (24 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-8621

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2020-8621

OS Trackers for CVE-2020-8621

vendor priority summary link
alpine high CVE-2020-8621: 1 source package rows (bind); 42 state rows across 10 repos (3.10-main, 3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 12, open 30. https://security.alpinelinux.org/vuln/CVE-2020-8621
debian not yet assigned CVE-2020-8621 not yet assigned priority: Debian including 1 source packages (bind9), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2020-8621
gentoo normal CVE-2020-8621: 1 GLSA(s) (202008-19), 1 atom(s) (net-dns/bind); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2020-8621
redhat medium — https://access.redhat.com/security/cve/CVE-2020-8621
suse high CVE-2020-8621 severity important: SUSE including 479 source package names (0.1.0:sysuser-shadow-2.0-4.2.8, 0.1.75:sysuser-shadow-2.0-4.2.8, …), 689 product×package rows across 182 product lines (Container bci/bci-init, Container bci/dotnet-aspnet, … (182 product lines)): Fixed 498, Known Affected 157, Known Not Affected 34. https://www.suse.com/security/cve/CVE-2020-8621/
ubuntu medium CVE-2020-8621 medium priority: Ubuntu including 1 source packages (bind9), 5 status rows across 5 suites (bionic, focal, trusty, upstream, xenial): not-affected 3, needs-triage 1, released 1. https://ubuntu.com/security/CVE-2020-8621

Affected software / configurations for CVE-2020-8621

Vendor Product Version Raw CPE
isc bind >= 9.14.0, <= 9.16.5 cpe:2.3:a:isc:bind:*:*:*:*:*:*:*:*
isc bind >= 9.17.0, <= 9.17.3 cpe:2.3:a:isc:bind:*:*:*:*:*:*:*:*
opensuse leap 15.1 cpe:2.3:o:opensuse:leap:15.1:*:*:*:*:*:*:*
opensuse leap 15.2 cpe:2.3:o:opensuse:leap:15.2:*:*:*:*:*:*:*
canonical ubuntu_linux 16.04 cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:esm:*:*:*
canonical ubuntu_linux 18.04 cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 20.04 cpe:2.3:o:canonical:ubuntu_linux:20.04:*:*:*:lts:*:*:*
synology dns_server < 2.2.2-5027 cpe:2.3:a:synology:dns_server:*:*:*:*:*:*:*:*
netapp steelstore_cloud_integrated_storage — cpe:2.3:a:netapp:steelstore_cloud_integrated_storage:-:*:*:*:*:*:*:*

References for CVE-2020-8621

cvelogic Threat Intelligence