Improper input validation in Tlsfuzzer Ecdsa
CVE-2026-33936
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.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.005 (42.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 42nd percentile — 42.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: +0.000
Affected products
- Tlsfuzzer Ecdsa
- Tlsfuzzer Python-Ecdsa — versions < 0.19.2
Weakness classification (CWE)
Public proof-of-concept exploits
References
- github.com/tlsfuzzer/python-ecdsa/security/advisories/GHSA-9f5j-8jwj-x28g (Exploit, Mitigation, Vendor Advisory)
- github.com/tlsfuzzer/python-ecdsa/commit/bd66899550d7185939bf27b75713a2ac9325a9… (Patch)
- github.com/tlsfuzzer/python-ecdsa/releases/tag/python-ecdsa-0.19.2 (Product, Release Notes)
Frequently asked questions
- What is CVE-2026-33936?
- CVE-2026-33936 is a medium-severity vulnerability in Tlsfuzzer Ecdsa, classified under Improper Input Validation. CVSS score: 5.3/10. Published 2026-03-27.
- How severe is CVE-2026-33936?
- Medium severity. CVSS v3 base score is 5.3 out of 10.
- Is CVE-2026-33936 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.