CVE-2021-43572: Starkbank ecdsa Improper Verification Of Cryptographic Signature Vulnerability

CRITICAL
Advisory Identifier: GHSA-92vm-mxjf-jqf3
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CVSS 9.8
CWE-347
Published
Advisory Summary

CVE-2021-43572 is a CRITICAL (CVSS 9.8) improper verification of cryptographic signature vulnerability (CWE-347: Improper Verification of Cryptographic Signature) affecting Starkbank ecdsa libraries in the PyPI ecosystem. The issue involves improper verification of cryptographic signature in starkbank-ecdsa. Remediation is available by upgrading affected packages to version 2.0.1.

CVE-2021-43572 at a Glance

CVE Identifier CVE-2021-43572
GHSA Identifier GHSA-92vm-mxjf-jqf3
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-347: Improper Verification of Cryptographic Signature
Affected Product Starkbank ecdsa
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 9.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2021-43572

To remediate this vulnerability, upgrade all affected Starkbank ecdsa dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

starkbank-ecdsa fixed: 2.0.1 
pip install starkbank-ecdsa>=2.0.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show starkbank-ecdsa

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-43572, inspect your installed packages using pip:

pip show starkbank-ecdsa

Analyze the terminal output to locate any version of Starkbank ecdsa in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.0.1), your application is affected.

Note: The pip show starkbank-ecdsa command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-347: Improper Verification of Cryptographic Signature, where the product does not verify, or incorrectly verifies, the cryptographic signature for data. In Starkbank ecdsa, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

The `verify` function in the Stark Bank Python ECDSA library (starkbank-ecdsa) 2.0.0 fails to check that the signature is non-zero, which allows attackers to forge signatures on arbitrary messages.

CVE-2021-43572 Affected Starkbank ecdsa Versions

1 component(s)
Fixed Versions:
2.0.1
Product / Package Ecosystem Affected Versions Fixed Version
starkbank-ecdsa
pypi/starkbank-ecdsa
PyPI
< 2.0.1
2.0.1

References

NVD — CVE-2021-43572 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-43572
Security Fix Commit FIX COMMIT
https://github.com/starkbank/ecdsa-python/commit/d136170666e9510eb63c2572551805807bd4c17f
Starkbank ecdsa Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/starkbank-ecdsa/PYSEC-2021-426.yaml
Starkbank ecdsa Source Repository REPOSITORY
https://github.com/starkbank/ecdsa-python
Starkbank ecdsa Release RELEASE
https://github.com/starkbank/ecdsa-python/releases/tag/v2.0.1
research.nccgroup.com/2021/11/08/technica... WEB
https://research.nccgroup.com/2021/11/08/technical-advisory-arbitrary-signature-forgery-in-stark-bank-ecdsa-libraries

Frequently Asked Questions

What is CVE-2021-43572?
CVE-2021-43572 is a security vulnerability in Starkbank ecdsa involving Improper Verification of Cryptographic Signature in starkbank-ecdsa under CWE-347: Improper Verification of Cryptographic Signature.
Which Starkbank ecdsa versions are affected?
Affected versions include releases prior to 2.0.1 across affected packages: starkbank-ecdsa.
What version fixes CVE-2021-43572?
Upgrading to 2.0.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is starkbank-ecdsa affected?
Yes, starkbank-ecdsa is affected in releases prior to 2.0.1. Upgrade your dependency to 2.0.1 or later.
What is the CVSS score of CVE-2021-43572?
CVE-2021-43572 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-43572?
CVE-2021-43572 is classified under CWE-347: Improper Verification of Cryptographic Signature (The product does not verify, or incorrectly verifies, the cryptographic signature for data.).
How can I check PyPI dependencies for CVE-2021-43572?
Run the dependency tree command: 'pip show starkbank-ecdsa'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-92vm-mxjf-jqf3",
  "modified" : "2024-10-25T14:49:40Z",
  "published" : "2021-11-10T20:41:39Z",
  "aliases" : [ "CVE-2021-43572" ],
  "summary" : "Improper Verification of Cryptographic Signature in starkbank-ecdsa",
  "details" : "The `verify` function in the Stark Bank Python ECDSA library (starkbank-ecdsa) 2.0.0 fails to check that the signature is non-zero, which allows attackers to forge signatures on arbitrary messages.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "starkbank-ecdsa"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.0.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-43572"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/starkbank/ecdsa-python/commit/d136170666e9510eb63c2572551805807bd4c17f"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/starkbank-ecdsa/PYSEC-2021-426.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/starkbank/ecdsa-python"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/starkbank/ecdsa-python/releases/tag/v2.0.1"
  }, {
    "type" : "WEB",
    "url" : "https://research.nccgroup.com/2021/11/08/technical-advisory-arbitrary-signature-forgery-in-stark-bank-ecdsa-libraries"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-347" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-11-10T18:23:18Z",
    "nvd_published_at" : "2021-11-09T22:15:00Z"
  }
}