# CVE-2021-20305: Other in nettle

> Attackers can cause denial of service or bypass signature validation in Nettle by exploiting out-of-range scalars in ECC operations.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 5 Apr 2021
- **Updated:** 14 Oct 2026
- **Also known as:** ALPINE-CVE-2021-20305, DEBIAN-CVE-2021-20305, GHSA-6xrq-2ww3-f6h5, JLSEC-2026-575, OESA-2021-1177, RHSA-2021:1145, RHSA-2021:1206, RHSA-2021:1245, RHSA-2021:1246, RHSA-2021:2280, RHSA-2021:2356, RHSA-2021:2758, RHSA-2021:2760, RLSA-2021:1206, SUSE-SU-2021:1399-1, SUSE-SU-2021:1412-1, UBUNTU-CVE-2021-20305, USN-4906-1, openSUSE-SU-2021:0635-1

## What is CVE-2021-20305?

CVE-2021-20305 is a high-severity vulnerability in Debian Debian Linux, published on 5 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-787 (Out-of-bounds Write), CWE-327 (Use of a Broken or Risky Cryptographic Algorithm)

## Which versions are affected by CVE-2021-20305?

It affects 6 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nettle` | Red Hat:enterprise_linux:7::client | All versions | 0:2.7.1-9.el7_9 |
| `nettle-debuginfo` | Red Hat:enterprise_linux:7::client | All versions | 0:2.7.1-9.el7_9 |
| `nettle-devel` | Red Hat:enterprise_linux:7::client | All versions | 0:2.7.1-9.el7_9 |
| `nettle-debuginfo` | Red Hat:enterprise_linux:7::computenode | All versions | 0:2.7.1-9.el7_9 |
| `nettle-devel` | Red Hat:enterprise_linux:7::computenode | All versions | 0:2.7.1-9.el7_9 |
| `nettle` | Red Hat:enterprise_linux:7::server | All versions | 0:2.7.1-9.el7_9 |
| `nettle-debuginfo` | Red Hat:enterprise_linux:7::server | All versions | 0:2.7.1-9.el7_9 |
| `nettle-devel` | Red Hat:enterprise_linux:7::server | All versions | 0:2.7.1-9.el7_9 |
| `nettle` | Red Hat:enterprise_linux:7::workstation | All versions | 0:2.7.1-9.el7_9 |
| `nettle-debuginfo` | Red Hat:enterprise_linux:7::workstation | All versions | 0:2.7.1-9.el7_9 |
| `nettle-devel` | Red Hat:enterprise_linux:7::workstation | All versions | 0:2.7.1-9.el7_9 |
| `gnutls-c++` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-c++-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-dane` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-dane-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-debugsource` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-devel` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-utils` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-utils-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.6.14-8.el8_3 |
| `nettle-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.4.1-4.el8_3 |
| `nettle-debugsource` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.4.1-4.el8_3 |
| `nettle-devel` | Red Hat:enterprise_linux:8::appstream | All versions | 0:3.4.1-4.el8_3 |
| `gnutls` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-c++-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-dane-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-debugsource` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.14-8.el8_3 |
| `gnutls-utils-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.6.14-8.el8_3 |
| `nettle` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.4.1-4.el8_3 |
| `nettle-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.4.1-4.el8_3 |
| `nettle-debugsource` | Red Hat:enterprise_linux:8::baseos | All versions | 0:3.4.1-4.el8_3 |
| `nettle` | Red Hat:rhel_aus:7.3::server | All versions | 0:2.7.1-9.el7_3 |
| `nettle-debuginfo` | Red Hat:rhel_aus:7.3::server | All versions | 0:2.7.1-9.el7_3 |
| `nettle-devel` | Red Hat:rhel_aus:7.3::server | All versions | 0:2.7.1-9.el7_3 |
| `nettle` | Red Hat:rhel_aus:7.4::server | All versions | 0:2.7.1-9.el7_4 |
| `nettle-debuginfo` | Red Hat:rhel_aus:7.4::server | All versions | 0:2.7.1-9.el7_4 |
| `nettle-devel` | Red Hat:rhel_aus:7.4::server | All versions | 0:2.7.1-9.el7_4 |
| `nettle` | Red Hat:rhel_aus:7.6::server | All versions | 0:2.7.1-9.el7_6 |
| `nettle-debuginfo` | Red Hat:rhel_aus:7.6::server | All versions | 0:2.7.1-9.el7_6 |

Products: Debian Debian Linux, Fedoraproject Fedora, Netapp Active Iq Unified Manager, Netapp Ontap Select Deploy Administration Utility, Nettle Project Nettle, Redhat Enterprise Linux.

## How do I fix CVE-2021-20305?

Upgrade to a fixed version.

## Is CVE-2021-20305 being exploited?

There is no known exploitation of CVE-2021-20305 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

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- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20305 and fix it if it is affected.

What it is: CVE-2021-20305 is a high-severity vulnerability in Debian Debian Linux, published on 5 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-20305 in the wild and no public exploit code.

Affected product: Debian Debian Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-20305/ (Markdown: https://insights.sbomify.com/CVE-2021-20305/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20305
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20305
- OSV: https://osv.dev/vulnerability/CVE-2021-20305

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20305/
Summaries are generated and may contain mistakes; the official description above is the record.