CVE-2026-33936 python-ecdsa: Denial of Service via improper DER length validation in crafted private keys
Attackers can cause denial of service in applications parsing untrusted DER private keys by triggering unhandled exceptions in the python-ecdsa library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33936?
CVE-2026-33936 is a medium-severity denial of service vulnerability in tlsfuzzer python-ecdsa, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-33936?
3 open source packages ship an affected version, including ecdsa. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
ecdsa PyPI | All versions | 0.19.2 |
ecdsa PyPI | All versions | 0.19.2 |
ecdsa PyPI | All versions | 0.19.2 |
Linux distribution packages (7)
python-ecdsa SUSE:Linux Enterprise Module for Basesystem 15 SP7 | All versions | 0.13.3-150000.3.10.1 |
python-ecdsa SUSE:Linux Enterprise Module for Python 3 15 SP7 | All versions | 0.18.0-150400.12.6.1 |
python-ecdsa SUSE:Linux Enterprise Server 16.0 | All versions | 0.19.1-160000.4.1 |
python-ecdsa SUSE:Linux Enterprise Server for SAP applications 16.0 | All versions | 0.19.1-160000.4.1 |
python-ecdsa openSUSE:Leap 15.6 | All versions | 0.18.0-150400.12.6.1 |
python-ecdsa openSUSE:Leap 16.0 | All versions | 0.19.1-160000.4.1 |
python-ecdsa openSUSE:Tumbleweed | All versions | 0.19.2-1.1 |
Products include Tlsfuzzer Ecdsa.
How do I fix CVE-2026-33936?
Upgrade ecdsa to 0.19.2 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-33936 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33936 exists.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in tlsfuzzer python-ecdsa
Sources
Also known as AZL-80975, CLEANSTART-2026-OH68688, DEBIAN-CVE-2026-33936, ECHO-dc11-daa6-fc93, GHSA-9f5j-8jwj-x28g, MINI-qcwf-3r36-gh33 and 14 more.