CVE-2021-20305Network attack vector

Signature bypass or crash via unreduced ECC scalars

Published Apr 5, 2021 · Updated Aug 3, 2024

Signature-verification flaws in GNU Nettle before 3.7.2 allow remote attackers to crash applications or accept invalid signatures. The ECDSA, GOST DSA, and EdDSA verification paths pass noncanonically reduced, out-of-range scalars into ECC multiplication and comparison routines. Reachability depends on a consuming application processing attacker-controlled signatures; consequences are bounded to assertion-triggered crashes or incorrect signature results.

CVSS severity8.1
High
EPSS probability1.69%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Signature-verification flaws in GNU Nettle before 3.7.2 allow remote attackers to crash applications or accept invalid signatures. The ECDSA, GOST DSA, and EdDSA verification paths pass noncanonically reduced, out-of-range scalars into ECC multiplication and comparison routines. Reachability depends on a consuming application processing attacker-controlled signatures; consequences are bounded to assertion-triggered crashes or incorrect signature results.

The record

CVE
CVE-2021-20305
Published
Apr 5, 2021
Updated
Aug 3, 2024
Vendor
GNU
Product
Nettle
Classifications
CWE-787
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=nettle 3.7.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

GNU · Nettleversion=nettle 3.7.2

Published CVSS scores

8.1UbuntuCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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