CVE-2026-33936
python-ecdsa: Denial of Service via improper DER length validation in crafted private keys
Description
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.
INFO
Published Date :
March 27, 2026, 11:17 p.m.
Last Modified :
Oct. 26, 2026, 10:10 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update the 'ecdsa' package to version 0.19.2.
- Handle unexpected exceptions from DER parsing.
- Validate untrusted DER private key inputs.
Public PoC/Exploit Available at Github
CVE-2026-33936 has a 2 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-33936.
| URL | Resource |
|---|---|
| https://github.com/tlsfuzzer/python-ecdsa/commit/bd66899550d7185939bf27b75713a2ac9325a9d3 | Patch |
| https://github.com/tlsfuzzer/python-ecdsa/releases/tag/python-ecdsa-0.19.2 | Product Release Notes |
| https://github.com/tlsfuzzer/python-ecdsa/security/advisories/GHSA-9f5j-8jwj-x28g | Exploit Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-33936 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-33936
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Denial of Service vulnerability in ecdsa (PyPI)
None
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-33936 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-33936 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Oct. 26, 2026
Action Type Old Value New Value Added Translation Title: python-ecdsa de tlsfuzzer, Description: El paquete “ecdsa” de PyPI es una implementación pura en Python de Criptografía de Curva Elíptica (ECC) con soporte para el Algoritmo de Firma Digital de Curva Elíptica (ECDSA), el Algoritmo de Firma Digital de Curva de Edwards (EdDSA) y Diffie-Hellman de Curva Elíptica (ECDH). Antes de la versión 0.19.2, un problema en las funciones de análisis DER de bajo nivel puede causar que se lancen excepciones inesperadas desde las funciones de la API pública. “ecdsa.der.remove_octet_string()” acepta DER truncado donde la longitud codificada excede el búfer disponible. Por ejemplo, una CADENA DE OCTETOS que declara una longitud de 4096 bytes pero proporciona solo 3 bytes se analiza correctamente en lugar de ser rechazada. Debido a esto, una entrada DER manipulada puede causar que “SigningKey.from_der()” lance una excepción interna (“IndexError: índice fuera de los límites en la dimensión 1”) en lugar de rechazar limpiamente el DER malformado (por ejemplo, lanzando “UnexpectedDER” o “ValueError”). Las aplicaciones que analizan claves privadas DER no confiables pueden fallar si no manejan las excepciones inesperadas, lo que resulta en una denegación de servicio. La versión 0.19.2 corrige el problema. -
CVE Modified by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'tlsfuzzer', 'product': 'python-ecdsa', 'versions': [{'status': 'affected', 'version': '< 0.19.2'}]}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-33936', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-04-01T13:44:27.418372Z'} -
Initial Analysis by [email protected]
Apr. 01, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:tlsfuzzer:ecdsa:*:*:*:*:*:python:*:* versions up to (excluding) 0.19.2 Added Reference Type GitHub, Inc.: https://github.com/tlsfuzzer/python-ecdsa/commit/bd66899550d7185939bf27b75713a2ac9325a9d3 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/tlsfuzzer/python-ecdsa/releases/tag/python-ecdsa-0.19.2 Types: Product, Release Notes Added Reference Type GitHub, Inc.: https://github.com/tlsfuzzer/python-ecdsa/security/advisories/GHSA-9f5j-8jwj-x28g Types: Exploit, Mitigation, Vendor Advisory -
New CVE Received by [email protected]
Mar. 27, 2026
Action Type Old Value New Value Added Description 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Added CWE CWE-20 Added CWE CWE-130 Added Reference https://github.com/tlsfuzzer/python-ecdsa/commit/bd66899550d7185939bf27b75713a2ac9325a9d3 Added Reference https://github.com/tlsfuzzer/python-ecdsa/releases/tag/python-ecdsa-0.19.2 Added Reference https://github.com/tlsfuzzer/python-ecdsa/security/advisories/GHSA-9f5j-8jwj-x28g