What is CVE-2021-43569?

CVE-2021-43569 is a critical-severity vulnerability in Starkbank Ecdsa-Dotnet, classified under Improper Verification of Cryptographic Signature. CVSS score: 9.8/10. Published 2021-11-09.

How severe is CVE-2021-43569?

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

Vulnerability in Starkbank Ecdsa-Dotnet

CVE-2021-43569

The verify function in the Stark Bank .NET ECDSA library (ecdsa-dotnet) 1.3.1 fails to check that the signature is non-zero, which allows attackers to forge signatures on arbitrary messages.

Published 2021-11-09 · 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: 0.011 (63.0th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 63rd percentile — 63.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.010 · newest: 0.011 · change: +0.000

Affected products

Starkbank Ecdsa-Dotnet — versions 1.3.2

Weakness classification (CWE)

CWE-347 — Improper Verification of Cryptographic Signature

References

research.nccgroup.com/2021/11/08/technical-advisory-arbitrary-signature-forgery… (Exploit, Third Party Advisory)
github.com/starkbank/ecdsa-dotnet/releases/tag/v1.3.2 (Third Party Advisory)

Frequently asked questions

What is CVE-2021-43569?: CVE-2021-43569 is a critical-severity vulnerability in Starkbank Ecdsa-Dotnet, classified under Improper Verification of Cryptographic Signature. CVSS score: 9.8/10. Published 2021-11-09.
How severe is CVE-2021-43569?: Critical severity. CVSS v3 base score is 9.8 out of 10.