What is CVE-2021-40818?

CVE-2021-40818 is a critical-severity vulnerability in Glewlwyd Sso Server Project, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2021-09-08.

How severe is CVE-2021-40818?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Glewlwyd Sso Server Project

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.

Vulnerability class: Buffer Overflow

Published 2021-09-08 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.015 (73.1th percentile), scored 2026-10-01.

Low probability of exploitation in the next 30 days, but still tracked. 73rd percentile — 73.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.015 · newest: 0.015 · change: +0.000

Affected products

Glewlwyd Sso Server Project

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)

References

github.com/babelouest/glewlwyd/commit/0efd112bb62f566877750ad62ee828bff579b4e2 (Patch, Third Party Advisory)
bugs.debian.org/993867 (Mailing List, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-40818?: CVE-2021-40818 is a critical-severity vulnerability in Glewlwyd Sso Server Project, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2021-09-08.
How severe is CVE-2021-40818?: Critical severity. CVSS v3 base score is 9.8 out of 10.