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Fencer Vulns
medium 5.3

CVE-2026-33936 json

python-ecdsa: Denial of Service via improper DER length validation in crafted private keys

published 2026-03-27 7 mo ago modified 2026-10-26 13 d ago also EUVD-2026-16856 , GHSA-9f5j-8jwj-x28g , PYSEC-2026-2467

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 42%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi ecdsa 0.19.2
  • tlsfuzzer ecdsa 0.19.2
  • python-ecdsa Debian 13 0.19.1-1+deb13u1
  • python-ecdsa Debian 14 0.19.2-1

debian advisories DEBIAN-CVE-2026-33936

  • python-ecdsa SLES for SAP applications 16.0, SLES 16.0 0.19.1-160000.4.1
  • python-ecdsa SLE Module for Basesystem 15 SP7 0.13.3-150000.3.10.1
  • python-ecdsa SLE Module for Python 3 15 SP7, openSUSE Leap 15.6 0.18.0-150400.12.6.1

suse advisories SUSE-SU-2026:22158-1SUSE-SU-2026:1608-1SUSE-SU-2026:1436-1

  • python-ecdsa openSUSE Leap 16.0 0.19.1-160000.4.1
  • python-ecdsa openSUSE Tumbleweed 0.19.2-1.1

opensuse advisories openSUSE-SU-2026:21078-1openSUSE-SU-2026:10468-1

  • python-ecdsa Azure Linux 3.0 0.19.2-1

azure linux advisories AZL-80975

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-33936 updated cvss 5.3

python-ecdsa: ecdsa: Denial of Service via crafted DER input

  • Red Hat Ansible Automation Platform 2 python-ecdsa
    affected: no fix planned “Out of support scope”
  • Red Hat Satellite 6 python-ecdsa, python3-ecdsa
    affected: no fix available “Fix deferred”
  • Red Hat Update Infrastructure 4 for Cloud Providers python-ecdsa
    affected: no fix planned “Out of support scope”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.48% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/tlsfuzzer/python-ecdsa/security/advisories/GHSA-9f5j-8jwj-x28g referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
OSV 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem package affected fixed in
pypi ecdsa
<0.19.2
0.19.2

Affected products

  • tlsfuzzer python-ecdsa

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-130 Improper Handling of Length Parameter Inconsistency

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.