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CRITICAL severity

CVE-2021-43572 — starkbank-ecdsa

CRITICALFix: starkbank/ecdsa-python@d136170

CVE-2021-43572 is a critical-severity (CVSS 9.8) CWE-347 vulnerability in starkbank-ecdsa. 1 public exploit reference exists, so weaponization risk is real. A fix is available for starkbank-ecdsa — see the affected versions and patch details below.

Improper Verification of Cryptographic Signature in starkbank-ecdsa

Also known asGHSA-92vm-mxjf-jqf3PYSEC-2021-426
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Oct 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs68th percentile — riskier than 68% of all scored CVEsHighest risk
0.00%0.58%1.17%1.75%0.2%1.2%May 26Sep 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-43572 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🐍starkbank-ecdsa

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

The verify function in the Stark Bank Python ECDSA library (aka starkbank-escada or ecdsa-python) before 2.0.1 fails to check that the signature is non-zero, which allows attackers to forge signatures on arbitrary messages.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIstarkbank-ecdsaall versions2.0.1pip install --upgrade 'starkbank-ecdsa==2.0.1'

Affected Products

1 product · 1 configurations
Application
ecdsa-pythonstarkbank
< 2.0.1
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

The verify function in the Stark Bank Python ECDSA library (aka starkban…

research.nccgroup.comNVDNov 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for starkbank-ecdsa, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update starkbank-ecdsa to 2.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43572 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

The verify function in the Stark Bank Python ECDSA library (aka starkbank-escada or ecdsa-python) before 2.0.1 fails to check that the signature is non-zero, which allows attackers to forge signatures on arbitrary messages.
O3 Security · Impact-Aware SCA

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CVE-2021-43572: starkbank-ecdsa — Fixed in 2.0.1