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CVE-2021-20305

26
FAUCET Score

CVE-2021-20305 is a critical vulnerability in Nettle versions prior to 3.7.2, impacting signature verification functions like GOST DSA, EDDSA, and ECDSA across products from Debian, Fedora, NetApp, and Red Hat. This flaw allows an attacker to manipulate Elliptic Curve Cryptography point multiplication with out-of-range scalers, potentially leading to incorrect results, assertion failures, or invalid signature validation. With a CVSS score of 8.1 (High), the vulnerability poses significant threats to confidentiality, integrity, and availability due to its network-based attack vector and high impact, despite high attack complexity. Currently, there is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 3.7.2CPE matchmatch criteria
cpe:2.3:a:nettle_project:nettle:*:*:*:*:*:*:*:*
33CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
7.0CPE matchmatch criteria
cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*
8.0CPE matchmatch criteria
cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:a:netapp:active_iq_unified_manager:-:*:*:*:*:vmware_vsphere:*:*

CVSS Data

CVSS version used by this source: 3.1

8.1HIGH

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.2
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.62%
Probability of exploitation in next 30 days
EPSS Percentile
73.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0162 is in the 31st percentile among its peer group of 8,918 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (20)

microsoftpatch availablevia msrc
Product: 19066-16820Fixed in: 3.7.2-1
microsoftpatch availablevia msrc
Product: cm1 nettle 3.7.2-1 on CBL Mariner 1.0Fixed in: 3.7.2-1
microsoftpatch availablevia msrc
Product: CBL Mariner 1.0 x64Fixed in: 3.7.2-1
microsoftpatch availablevia msrc
Product: CBL Mariner 1.0 ARMFixed in: 3.7.2-1
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.4 Telco Extended Update SupportFixed in: nettle-0:2.7.1-9.el7_4
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.4 Update Services for SAP SolutionsFixed in: nettle-0:2.7.1-9.el7_4
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.6 Advanced Update Support(Disable again in 2026 - SPRHEL-7118)Fixed in: nettle-0:2.7.1-9.el7_6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.6 Telco Extended Update SupportFixed in: nettle-0:2.7.1-9.el7_6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.6 Update Services for SAP SolutionsFixed in: nettle-0:2.7.1-9.el7_6
View patch
redhatpatch availablevia nvd_reference
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: gnutls-0:3.6.14-8.el8_3
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: nettle-0:3.4.1-4.el8_3
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.1 Extended Update SupportFixed in: gnutls-0:3.6.8-10.el8_1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.1 Extended Update SupportFixed in: nettle-0:3.4.1-2.el8_1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.2 Extended Update SupportFixed in: gnutls-0:3.6.8-12.el8_2
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.2 Extended Update SupportFixed in: nettle-0:3.4.1-2.el8_2
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.7 Extended Update SupportFixed in: nettle-0:2.7.1-9.el7_7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: nettle-0:2.7.1-9.el7_9
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.3 Advanced Update SupportFixed in: nettle-0:2.7.1-9.el7_3
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.4 Advanced Update SupportFixed in: nettle-0:2.7.1-9.el7_4
View patch

Vendor Advisories (3)

microsoft2023-Mar/CVE-2021-20305

CVE-2021-20305

Mar 14, 2023
microsoft2021-Apr/CVE-2021-20305Important

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.

Apr 13, 2021
redhatCVE-2021-20305Important

nettle: Out of bounds memory access in signature verification

Mar 16, 2021

References

bugzilla.redhat.com / show_bug.cgi
Issue TrackingPatchThird Party Advisory
lists.debian.org / debian-lts-announce/2021/09/msg00008.html
Mailing ListThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/MQKWVVMAIDAJ7YAA3VVO32BHLDOH2E63
security.gentoo.org / glsa/202105-31
Third Party Advisory
security.netapp.com / advisory/ntap-20211022-0002
Third Party Advisory
debian.org / security/2021/dsa-4933
Third Party Advisory