CVE-2021-20718 [High] | Denial of Service in Mod Auth Openidc

CVE-2021-20718 is rated Moderate Risk (57.7/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.85%). Review affected assets and schedule remediation.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-12-30	3.06%	1.85%	-1.21%
2	2025-11-21	1.75%	3.06%	+1.31%
3	2025-11-18	—	1.75%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-12-30

3.06%

1.85%

-1.21%

2025-11-21

1.75%

3.06%

+1.31%

2025-11-18

—

1.75%

—

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]
5.0	2.0	MEDIUM	`AV:N/AC:L/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:L) Exploitation conditions are straightforward and predictable. 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.	10.0	2.9	[email protected]

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]

5.0

2.0

MEDIUM

AV:N/AC:L/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:L): Exploitation conditions are straightforward and predictable.
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.

10.0

2.9

[email protected]

OS Trackers for CVE-2021-20718

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2021-20718 not yet assigned priority: Debian including 1 source packages (libapache2-mod-auth-openidc), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-20718
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2021-20718
`suse`	high	CVE-2021-20718 severity important: SUSE including 2 source package names (apache2-mod_auth_openidc, apache2-mod_auth_openidc-2.4.0-3.14.1), 17 product×package rows across 17 product lines (SUSE CaaS Platform 4.0, SUSE Enterprise Storage 6, … (17 product lines)): Known Not Affected 10, Fixed 7.	https://www.suse.com/security/cve/CVE-2021-20718/
`ubuntu`	medium	CVE-2021-20718 medium priority: Ubuntu including 1 source packages (libapache2-mod-auth-openidc), 16 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 11, ignored 2, DNE 1, needed 1, released 1.	https://ubuntu.com/security/CVE-2021-20718

Affected software / configurations for CVE-2021-20718

Vendor	Product	Version	Raw CPE
openidc	mod_auth_openidc	>= 2.4.0, <= 2.4.7	cpe:2.3:a:openidc:mod_auth_openidc::::::::
fedoraproject	fedora	33	cpe:2.3:o:fedoraproject:fedora:33:::::::*
fedoraproject	fedora	34	cpe:2.3:o:fedoraproject:fedora:34:::::::*
oracle	essbase	< 21.3	cpe:2.3:a:oracle:essbase::::::::

References for CVE-2021-20718

URL	Tags
https://github.com/zmartzone/mod_auth_openidc	Product Third Party Advisory
https://jvn.jp/en/jp/JVN49704918/index.html	Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5HJK366TLFEOIYWTHQSZO24MSDPBXHJU/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FV4KYMQWPS3I2QPW2C253MLIAFGBZPLK/
https://www.oracle.com/security-alerts/cpujan2022.html	Third Party Advisory
https://www.zmartzone.eu/	Vendor Advisory

URL

CVE-2021-20718

Exploit prediction scoring system (EPSS) score for CVE-2021-20718

Common vulnerability scoring system (CVSS) metrics for CVE-2021-20718

Weakness enumeration for CVE-2021-20718

OS Trackers for CVE-2021-20718

Affected software / configurations for CVE-2021-20718

References for CVE-2021-20718