# CVE-2026-33936: PYSEC-2026-2467 - python-ecdsa: Denial of Service via improper DER length validation in crafted private keys

Source: https://junglewise.ai/threats/cve-2026-33936-python-ecdsa-denial-of-service-via-improper-der-length-validation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-27  
License: CC BY 4.0 with a link back

CVE-2026-33936 · Severity: medium · CVSS 5.3 · Published 2026-03-27

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.

Technologies: [ecdsa (PyPI)](https://junglewise.ai/threats/technologies/ecdsa). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-33936 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-33936 being exploited in the wild.

**How severe is CVE-2026-33936?** Medium severity, with a CVSS score of 5.3, published 27 March 2026.

**Which products and versions are affected?** ecdsa (PyPI) ECOSYSTEM:introduced=0,fixed=0.19.2.

**Is there a fix for CVE-2026-33936?** Yes. ecdsa (PyPI): upgrade to 0.19.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-33936?** Check whether you run ecdsa (PyPI) or Tlsfuzzer Ecdsa at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- ecdsa (PyPI): upgrade to 0.19.2 or later

  ```sh
  pip install "ecdsa>=0.19.2"
  ```


## Affected products

- ecdsa (PyPI) ECOSYSTEM:introduced=0,fixed=0.19.2
- Tlsfuzzer Ecdsa

## Identifiers

- CVE-2026-33936
- GHSA-9f5j-8jwj-x28g
- PYSEC-2026-2467

## Related threats

- [PYSEC-2026-1325 - Minerva timing attack on P-256 in python-ecdsa](https://junglewise.ai/threats/cve-2024-23342-minerva-timing-attack-on-p-256-in-python-ecdsa)
- [Improper Verification of Cryptographic Signature in Pure-Python ECDSA](https://junglewise.ai/threats/cve-2019-14859-improper-verification-of-cryptographic-signature-in-pure-python)
- [PYSEC-2020-182 - A flaw was found in all python-ecdsa versions before 0.13.3, where it did not correctly verify…](https://junglewise.ai/threats/pysec-2020-182-a-flaw-was-found-in-all-python-ecdsa-versions-before-0-bee0e6ea)
- [ecdsa Denial of Service vulnerability in signature verification and signature malleability](https://junglewise.ai/threats/cve-2019-14853-python-ecdsa-malformed-signature-denial-of-service)