python-ecdsa: Denial of Service via improper DER length validation in crafted private keys

MITRE NVD CVE.ORG Print: PDF PDF

Summary

CVECVE-2026-33936
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-27 23:17:13 UTC
Updated2026-04-01 13:23:21 UTC
DescriptionThe `ecdsa` PyPI package is a pure Python implementation of ECC (Elliptic Curve Cryptography) with support for ECDSA (Elliptic Curve Digital Signature Algorithm), EdDSA (Edwards-curve Digital Signature Algorithm) and ECDH (Elliptic Curve Diffie-Hellman). Prior to version 0.19.2, an issue in the low-level DER parsing functions can cause unexpected exceptions to be raised from the public API functions. `ecdsa.der.remove_octet_string()` accepts truncated DER where the encoded length exceeds the available buffer. For example, an OCTET STRING that declares a length of 4096 bytes but provides only 3 bytes is parsed successfully instead of being rejected. Because of that, a crafted DER input can cause `SigningKey.from_der()` to raise an internal exception (`IndexError: index out of bounds on dimension 1`) rather than cleanly rejecting malformed DER (e.g., raising `UnexpectedDER` or `ValueError`). Applications that parse untrusted DER private keys may crash if they do not handle unexpected exceptions, resulting in a denial of service. Version 0.19.2 patches the issue.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS: 0.000470000 probability, percentile 0.144500000 (date 2026-04-01)

Problem Types: CWE-20 | CWE-130 | CWE-20 CWE-20: Improper Input Validation | CWE-130 CWE-130: Improper Handling of Length Parameter Inconsistency

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNADECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Tlsfuzzer Ecdsa All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Tlsfuzzer Python-ecdsa affected < 0.19.2 Not specified

References

ReferenceSourceLinkTags
github.com/tlsfuzzer/python-ecdsa/commit/bd66899550d7185939bf27b75713a2a... [email protected] github.com Patch
github.com/tlsfuzzer/python-ecdsa/security/advisories/GHSA-9f5j-8jwj-x28g [email protected] github.com Exploit, Mitigation, Vendor Advisory
github.com/tlsfuzzer/python-ecdsa/releases/tag/python-ecdsa-0.19.2 [email protected] github.com Product, Release Notes
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis
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