CVE-2021-40818

scheme/webauthn.c in Glewlwyd SSO server through 2.5.3 has a buffer overflow during FIDO2 signature validation in webauthn registration.

Published: 2021-09-08 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-40818 is rated Moderate Risk (64/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 1.48%). 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-2021-40818

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 2026-07-02 1.43% 1.48% +0.05%
2 2026-06-15 0.46% 1.43% +0.98%
3 2025-11-21 — 0.46% —

Full EPSS history (12 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-40818

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/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:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-40818

OS Trackers for CVE-2021-40818

vendor priority summary link
debian not yet assigned CVE-2021-40818 not yet assigned priority: Debian including 1 source packages (glewlwyd), 3 status rows across 3 suites (bookworm, bullseye, trixie): resolved 3. https://security-tracker.debian.org/tracker/CVE-2021-40818
ubuntu medium CVE-2021-40818 medium priority: Ubuntu including 1 source packages (glewlwyd), 15 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): ignored 6, not-affected 6, DNE 1, needs-triage 1, released 1. https://ubuntu.com/security/CVE-2021-40818

Affected software / configurations for CVE-2021-40818

Vendor Product Version Raw CPE
glewlwyd_sso_server_project glewlwyd_sso_server <= 2.5.3 cpe:2.3:a:glewlwyd_sso_server_project:glewlwyd_sso_server:*:*:*:*:*:*:*:*

References for CVE-2021-40818

URL Tags
https://bugs.debian.org/993867 Issue Tracking Mailing List Third Party Advisory
https://github.com/babelouest/glewlwyd/commit/0efd112bb62f566877750ad62ee828bff579b4e2 Patch Third Party Advisory
cvelogic Threat Intelligence