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 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.

Published: 2021-04-05 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-20305 is rated Moderate Risk (44.4/100): CVSS High severity, with low exploitation likelihood (EPSS 0.14%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-20305

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-29 0.20% 0.14% -0.06%
2 2025-12-05 0.28% 0.20% -0.08%
3 2025-11-21 — 0.28% —

Full EPSS history (25 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-20305

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.1 3.1 HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 5.9 [email protected]
6.8 2.0 MEDIUM
AV:N/AC:M/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 6.4 [email protected]

Weakness enumeration for CVE-2021-20305

OS Trackers for CVE-2021-20305

vendor priority summary link
alpine high CVE-2021-20305: 1 source package rows (nettle); 10 state rows across 10 repos (3.10-main, 3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 7, open 3. https://security.alpinelinux.org/vuln/CVE-2021-20305
debian not yet assigned CVE-2021-20305 not yet assigned priority: Debian including 1 source packages (nettle), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-20305
gentoo low CVE-2021-20305: 1 GLSA(s) (202105-31), 1 atom(s) (dev-libs/nettle); latest impact low. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-20305
redhat high — https://access.redhat.com/security/cve/CVE-2021-20305
suse high CVE-2021-20305 severity important: SUSE including 418 source package names (0.1.0:libhogweed4-3.4.1-4.15.1, 0.1.0:libnettle6-3.4.1-4.15.1, …), 733 product×package rows across 177 product lines (Container caasp/v4/389-ds, Container caasp/v4/busybox, … (177 product lines)): Fixed 576, Known Affected 137, Known Not Affected 20. https://www.suse.com/security/cve/CVE-2021-20305/
ubuntu medium CVE-2021-20305 medium priority: Ubuntu including 1 source packages (nettle), 16 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): released 15, needed 1. https://ubuntu.com/security/CVE-2021-20305

Affected software / configurations for CVE-2021-20305

Vendor Product Version Raw CPE
nettle_project nettle < 3.7.2 cpe:2.3:a:nettle_project:nettle:*:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
redhat enterprise_linux 7.0 cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
netapp active_iq_unified_manager — cpe:2.3:a:netapp:active_iq_unified_manager:-:*:*:*:*:vmware_vsphere:*:*
netapp ontap_select_deploy_administration_utility — cpe:2.3:a:netapp:ontap_select_deploy_administration_utility:-:*:*:*:*:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

References for CVE-2021-20305

cvelogic Threat Intelligence