CVE-2021-43572Public exploitNetwork attack vector

Arbitrary signature forgery via missing range checks

Published Nov 9, 2021 · Updated Aug 4, 2024

Improper signature verification in Stark Bank Python ECDSA before 2.0.1 allows attackers to forge signatures via zero-valued components. The verify function accepts r and s without enforcing the required 1-to-n-minus-1 range; Math.inv returns zero for s=0, so the final comparison reduces to 0==0. Any caller that trusts the library's Boolean result can accept an arbitrary message under any public key, bypassing the application's signature-based trust decision.

CVSS severity9.8
Critical
EPSS probability1.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper signature verification in Stark Bank Python ECDSA before 2.0.1 allows attackers to forge signatures via zero-valued components. The verify function accepts r and s without enforcing the required 1-to-n-minus-1 range; Math.inv returns zero for s=0, so the final comparison reduces to 0==0. Any caller that trusts the library's Boolean result can accept an arbitrary message under any public key, bypassing the application's signature-based trust decision.

The record

CVE
CVE-2021-43572
Published
Nov 9, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-347
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/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

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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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 exploitPublished

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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