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Fencer Vulns
high 8.1

CVE-2021-20305 json

A flaw was found in Nettle in versions before 3.7.2, where several Nettle signature verification functions (GOST DSA, EDDSA & ECDSA) result…

published 2021-04-05 5 y ago modified 2026-10-14 26 d ago also EUVD-2021-7730 , JLSEC-2026-575

cvss
8.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.7%
EPSS 1.7% chance of exploitation in 30 days, percentile 76%
public exploits
0
none known

Summary

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.

Patch / fix

  • julia Nettle_jll 3.7.2+0
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • nettle Debian 14, Debian 13, Debian 12 3.7.2-1

debian advisories DEBIAN-CVE-2021-20305

  • nettle Ubuntu 16.04 LTS 3.2-1ubuntu0.16.04.2
  • nettle Ubuntu 18.04 LTS 3.4-1ubuntu0.1
  • nettle Ubuntu 20.04 LTS 3.5.1+really3.5.1-2ubuntu0.1

ubuntu advisories UBUNTU-CVE-2021-20305

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • gnutls RHEL 8 3.6.14-8.el8_3
  • nettle RHEL 8 3.4.1-4.el8_3
  • gnutls-c++ RHEL 8 3.6.14-8.el8_3
  • gnutls-dane RHEL 8 3.6.14-8.el8_3
  • gnutls-utils RHEL 8 3.6.14-8.el8_3
  • nettle RHEL 7 2.7.1-9.el7_9
  • nettle RHEL 7.3 AUS 2.7.1-9.el7_3
  • nettle RHEL 7.4 TUS, RHEL 7.4 E4S, RHEL 7.4 AUS 2.7.1-9.el7_4

red hat advisories RHSA-2021:2760RHSA-2021:2758RHSA-2021:2356RHSA-2021:2280RHSA-2021:1245RHSA-2021:1246

  • libnettle SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +12 more 3.4.1-4.15.1
  • libnettle SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +11 more 2.7.1-13.3.1

suse advisories SUSE-SU-2021:1412-1SUSE-SU-2021:1399-1

  • libnettle openSUSE Leap 15.2 3.4.1-lp152.4.3.1

opensuse advisories openSUSE-SU-2021:0635-1

  • gnutls Rocky Linux 8 3.6.14-8.el8_3
  • nettle Rocky Linux 8 3.4.1-4.el8_4

rocky linux advisories RLSA-2021:1206

  • nettle Alpine 3.24, Alpine 3.23, Alpine 3.22 +9 more 3.7.2-r0

alpine advisories ALPINE-CVE-2021-20305

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • nettle Arch Linux 3.7.2-1

arch linux advisories AVG-1763

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-20305 updated cvss 8.1

nettle: Out of bounds memory access in signature verification

  • Red Hat Enterprise Linux AppStream (v. 8) gnutls-c++ 3.6.14-8.el8_3, gnutls-dane 3.6.14-8.el8_3, gnutls-utils 3.6.14-8.el8_3
    fixed: vendor fix RHSA-2021:1206
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) gnutls-c++ 3.6.8-10.el8_1, gnutls-dane 3.6.8-10.el8_1, gnutls-utils 3.6.8-10.el8_1
    fixed: vendor fix RHSA-2021:1245
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) gnutls-c++ 3.6.8-12.el8_2, gnutls-dane 3.6.8-12.el8_2, gnutls-utils 3.6.8-12.el8_2
    fixed: vendor fix RHSA-2021:1246
  • Red Hat Enterprise Linux BaseOS (v. 8) nettle 3.4.1-4.el8_3, gnutls 3.6.14-8.el8_3
    fixed: vendor fix RHSA-2021:1206
  • Red Hat Enterprise Linux BaseOS EUS (v. 8.1) nettle 3.4.1-2.el8_1, gnutls 3.6.8-10.el8_1
    fixed: vendor fix RHSA-2021:1245
  • Red Hat Enterprise Linux BaseOS EUS (v. 8.2) nettle 3.4.1-2.el8_2, gnutls 3.6.8-12.el8_2
    fixed: vendor fix RHSA-2021:1246
  • Red Hat Enterprise Linux Client (v. 7) nettle 2.7.1-9.el7_9 Red Hat Enterprise Linux Client Optional (v. 7) nettle-devel 2.7.1-9.el7_9, nettle-debuginfo 2.7.1-9.el7_9
    fixed: vendor fix RHSA-2021:1145
  • Red Hat Enterprise Linux ComputeNode EUS (v. 7.7) nettle 2.7.1-9.el7_7
    fixed: vendor fix RHSA-2021:2280
show 13 more
  • Red Hat Enterprise Linux ComputeNode Optional (v. 7) nettle-devel 2.7.1-9.el7_9, nettle-debuginfo 2.7.1-9.el7_9
    fixed: vendor fix RHSA-2021:1145
  • Red Hat Enterprise Linux ComputeNode Optional EUS (v. 7.7) nettle-devel 2.7.1-9.el7_7, nettle-debuginfo 2.7.1-9.el7_7
    fixed: vendor fix RHSA-2021:2280
  • Red Hat Enterprise Linux Server (v. 7) nettle 2.7.1-9.el7_9
    fixed: vendor fix RHSA-2021:1145
  • Red Hat Enterprise Linux Server AUS (v. 7.3) nettle 2.7.1-9.el7_3
    fixed: vendor fix RHSA-2021:2760
  • Red Hat Enterprise Linux Server AUS (v. 7.4) nettle 2.7.1-9.el7_4
    fixed: vendor fix RHSA-2021:2758
  • Red Hat Enterprise Linux Server AUS (v. 7.6) nettle 2.7.1-9.el7_6
    fixed: vendor fix RHSA-2021:2356
  • Red Hat Enterprise Linux Server E4S (v. 7.4) nettle 2.7.1-9.el7_4
    fixed: vendor fix RHSA-2021:2758
  • Red Hat Enterprise Linux Server E4S (v. 7.6) nettle 2.7.1-9.el7_6
    fixed: vendor fix RHSA-2021:2356
  • Red Hat Enterprise Linux Server EUS (v. 7.7) nettle 2.7.1-9.el7_7
    fixed: vendor fix RHSA-2021:2280
  • Red Hat Enterprise Linux Server TUS (v. 7.4) nettle 2.7.1-9.el7_4
    fixed: vendor fix RHSA-2021:2758
  • Red Hat Enterprise Linux Server TUS (v. 7.6) nettle 2.7.1-9.el7_6
    fixed: vendor fix RHSA-2021:2356
  • Red Hat Enterprise Linux Workstation (v. 7) nettle 2.7.1-9.el7_9
    fixed: vendor fix RHSA-2021:1145
  • Red Hat Enterprise Linux 9 nettle Red Hat OpenStack Platform 10 (Newton) nettle Red Hat OpenStack Platform 13 (Queens) nettle Red Hat OpenStack Platform 16.1 nettle
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-23-348-10 updated cvss 8.1

Siemens SIMATIC S7-1500

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.0, < 3.1.5
    affected: fixed in V3.1.5, mitigation support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

1.67% chance of exploitation in the next 30 days, higher than 76% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P
OSV 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
julia Nettle_jll
<3.7.2+0
3.7.2+0

Affected products

  • n/a nettle
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness
  • CWE-327 Use of a Broken or Risky Cryptographic Algorithm
  • CWE-787 Out-of-bounds Write

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.