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CVE-2020-12607

Improper Verification of Cryptographic Signature in fastecdsa

7.5 HighFix available

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s^-1, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

1.31%Up 0.3 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used 7.5

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s^-1, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

Record
CVE-2020-12607
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:P/I:N/A:N
Weakness
CWE-347
Updated
2026-11-02
CVE List No score

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s^-1, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

Record
CVE-2020-12607
Updated
2026-11-02
EUVDEUVD-2020-0078 No score

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s^-1, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

Record
EUVD-2020-0078
Updated
2026-11-03
GitHub AdvisoriesGHSA-56wv-2wr9-3h9r 8.7

Improper Verification of Cryptographic Signature in fastecdsa

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s<sup>-1</sup>, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

Record
GHSA-56wv-2wr9-3h9r
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-347
Updated
2026-11-02
OSV 7.5

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s^-1, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

Record
CVE-2020-12607
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVGHSA-56wv-2wr9-3h9r 8.7

Improper Verification of Cryptographic Signature in fastecdsa

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s<sup>-1</sup>, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

Record
GHSA-56wv-2wr9-3h9r
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-347
Updated
2026-11-02
OSVPYSEC-2020-42 No score

An issue was discovered in fastecdsa before 2.1.2. When using the NIST P-256 curve in the ECDSA implementation, the point at infinity is mishandled. This means that for an extreme value in k and s^-1, the signature verification fails even if the signature is correct. This behavior is not solely a usability problem. There are some threat models where an attacker can benefit by successfully guessing users for whom signature verification will fail.

Record
PYSEC-2020-42
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
fastecdsa
PyPI
before 2.1.2
2.1.2
fastecdsa
PyPI
before 2.1.2, plus listed versions
1.0.0b11.0.11.0.1b11.0.1b21.0.1b3
Show 28 moreShow less
1.0.21.0.31.1.01.1.11.1.21.1.31.2.11.3.11.3.21.4.11.4.21.4.31.5.11.5.21.6.11.6.21.6.31.6.41.6.51.7.01.7.11.7.21.7.31.7.41.7.52.0.02.1.02.1.1
2.1.2
fastecdsa
PyPI
before 2.1.2, plus listed versions
1.0.0b11.0.1b11.0.1b21.0.1b31.0.1
Show 28 moreShow less
1.0.21.0.31.1.01.1.11.1.21.1.31.2.11.3.11.3.21.4.11.4.21.4.31.5.11.5.21.6.11.6.21.6.31.6.41.6.51.7.01.7.11.7.21.7.31.7.41.7.52.0.02.1.02.1.1
2.1.2

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2020-12607 is a high vulnerability (CVSS 7.5) in Antonkueltz Fastecdsa, published June 2, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.31%, the 70th percentile. Fixed in fastecdsa 2.1.2.

References

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