CVE-2021-43569: The verify function in the Stark Bank .NET ECDSA library (ecdsa-dotnet) 1.3.1 fails to check that the signatur

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CRITICAL 9.8REMOTEDOWNGRADE

CVE-2021-43569 is a critical-severity flaw (CVSS 9.8) affecting ecdsa-dotnet. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.1% (top 36%)
CISA exploited list	No
Weakness	CWE-347
Published	2021-11-09
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: starkbank

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-11-09 22:15 UTCPublished CVE record published
2026-06-17 04:11 UTCUpdated Record last modified

starkbank ecdsa-dotnet DOWNGRADE

Affected: 1.3.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.3.2

1. Check installed version

apt-cache policy ecdsa-dotnet || rpm -q ecdsa-dotnet || ecdsa-dotnet --version

2. No fixed release: DOWNGRADE to a release before 1.3.2 (Debian / Ubuntu)

apt-cache madison ecdsa-dotnet sudo apt install ecdsa-dotnet=<VERSION_BEFORE_1.3.2> sudo apt-mark hold ecdsa-dotnet

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list ecdsa-dotnet sudo dnf downgrade ecdsa-dotnet-<VERSION_BEFORE_1.3.2> sudo dnf versionlock add ecdsa-dotnet

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-43569?

ecdsa-dotnet: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-43569 being exploited?

CVE-2021-43569 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-43569 affect?

CVE-2021-43569 affects ecdsa-dotnet. Severity is critical (CVSS 9.8). 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.

How urgent is CVE-2021-43569?

Priority 60/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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