Summaryinfo

A vulnerability, which was classified as problematic, has been found in tlsfuzzer python-ecdsa up to 0.19.1. This issue affects the function ECDSA.der.remove_octet_string. This manipulation causes denial of service. This vulnerability is handled as CVE-2026-33936. The attack can be initiated remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in tlsfuzzer python-ecdsa up to 0.19.1. Affected by this vulnerability is the function ECDSA.der.remove_octet_string. The manipulation with an unknown input leads to a denial of service vulnerability. The CWE definition for the vulnerability is CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. As an impact it is known to affect availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-33936 since 03/24/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 304163 (Linux Distros Unpatched Vulnerability : CVE-2026-33936), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 0.19.2 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (304163) and EUVD (EUVD-2026-16856). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Programming Language Software

Vendor

• tlsfuzzer

Name

• python-ecdsa

Version

• 0.19.0
• 0.19.1

Website

• Product: https://github.com/tlsfuzzer/python-ecdsa/

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