CVE-2021-20305

Name: CVE-2021-20305
Creator: NVD / NIST
Published: 2021-04-05T22:15:12.727+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.1/10EPSS 1.61%

Last modified Jun 17, 2026

CVE-2021-20305 is a high-severity vulnerability rated 8.1/10 on the CVSS scale. 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. EPSS estimates a 1.61% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

8.1/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

1.61%

72.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Nettle Project	Nettle	< 3.7.2
Fedoraproject	Fedora	33
Redhat	Enterprise Linux	7.0
Redhat	Enterprise Linux	8.0
Netapp	Active Iq Unified Manager	All versions
Netapp	Ontap Select Deploy Administration Utility	All versions
Debian	Debian Linux	9.0
Debian	Debian Linux	10.0

References

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

Timeline

Published: Apr 5, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-20305?

How severe is CVE-2021-20305?

CVE-2021-20305 has a CVSS score of 8.1/10 (HIGH severity). The EPSS model estimates a 1.61% probability of exploitation in the next 30 days.

How do I fix CVE-2021-20305?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-20305?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST