CVE-2026-33936 (GCVE-0-2026-33936)

Vulnerability from cvelistv5 – Published: 2026-03-27 22:08 – Updated: 2026-04-01 13:44
VLAI Previdian
Title
python-ecdsa: Denial of Service via improper DER length validation in crafted private keys
Summary
The `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.
Severity
5.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
SSVC
Exploitation: poc Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-04-01 13:44 UTC
CWE
  • CWE-20 - Improper Input Validation
  • CWE-130 - Improper Handling of Length Parameter Inconsistency
Assigner
GitHub_M CNA under the mitre root
CNA scorecard C 72/100 over 7617 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
tlsfuzzer python-ecdsa Affected: < 0.19.2
guessed Create a notification for this product.
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 17604779-a4ab-4f40-ac88-aedbc87c9b0f

Vulnerability ID: CVE-2026-33936

Status: Confirmed

Status Updated: 2026-04-02 09:00 UTC

Exploited: Yes

Timestamps
First Seen: 2026-04-02
Asserted: 2026-04-02
Scope
Notes: KEVIntel entry: python-ecdsa: Denial of Service via improper DER length validation in crafted private keys | Affected: tlsfuzzer / python-ecdsa | CVSS: 5.3 (MEDIUM) | Used in malware: unknown | Not yet in CISA KEV: True
Evidence

Type: Public Report

Signal: Successful Exploitation

Confidence: 70%

Source: kevintel

Details
Feed KEVIntel (kevintel.com)
Title python-ecdsa: Denial of Service via improper DER length validation in crafted private keys
Vendor tlsfuzzer
Product python-ecdsa
Added Date 2026-04-02T09:00:05.000Z
Cvss Score 5.3
Epss Score None
Cvss Severity MEDIUM
Epss Percentile None
Used In Malware unknown
Ahead Of Cisa Kev None
Not Yet In Cisa Kev True
References
Created: 2026-06-19 12:42 UTC | Updated: 2026-06-19 12:42 UTC
Show details on NVD website
To clipboard 

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