How severe is CVE-2021-40818?

CVE-2021-40818 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-40818 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40818?

CVE-2021-40818 affects Glewlwyd Sso Server Project Glewlwyd Sso Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40818?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-40818 published?

CVE-2021-40818 was published on 2021-09-08 and last updated on 2026-06-17.

CVE-2021-40818

CVE-2021-40818 is a critical-severity vulnerability in Glewlwyd Sso Server Project Glewlwyd Sso Server with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-120.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 1% (71st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-120
Affected product: Glewlwyd Sso Server Project Glewlwyd Sso Server
Published: 2021-09-08
Last modified: 2026-06-17

Description

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

Frequently asked questions

What is 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.
How severe is CVE-2021-40818?: CVE-2021-40818 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-40818 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40818?: CVE-2021-40818 affects Glewlwyd Sso Server Project Glewlwyd Sso Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40818?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-40818 published?: CVE-2021-40818 was published on 2021-09-08 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:glewlwyd_sso_server_project:glewlwyd_sso_server:*:*:*:*:*:*:*:*

More vulnerabilities in Glewlwyd Sso Server Project Glewlwyd Sso Server

CVE-2023-49208 — Critical (CVSS 9.8): scheme/webauthn.c in Glewlwyd SSO server before 2.7.6 has a possible buffer overflow during FIDO2 credentials…
CVE-2022-27240 — Critical (CVSS 9.8): scheme/webauthn.c in Glewlwyd SSO server 2.x before 2.6.2 has a buffer overflow associated with a webauthn assertion.
CVE-2024-25715 — Medium (CVSS 6.1): Glewlwyd SSO server 2.x through 2.7.6 allows open redirection via redirect_uri.

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