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Exploitation reportedNot in CISA KEV yetFix available

CVE-2026-33936

Exploitation reported by one source. First attested on 2026-04-02 by GCVE · kevintel.

  • Published2026-03-27
  • Fixed in0.19.2
  • WeaknessCWE-130 · CWE-20

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2026-03-2723:17CVE publishedNVD
  2. 2026-04-0209:00Listed as exploited by GCVEGCVE
  3. 2026-04-0209:00Exploitation first reportedGCVE
  4. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-33936?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-33936?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Tlsfuzzer ecdsa
BranchAffectedFixed in
0.19< 0.19.20.19.2

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Tlsfuzzer ecdsa to 0.19.2

Advisories and patches

Detection

read 2026-10-23 19:25 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverified0xmrma/CVE-2026-33936
PoC-in-GitHub

Sources

  • NVDCVE recordread 2026-10-23
  • GCVEexploitation2026-04-02
  • CISA-ADPSSVC decisionpoc2026-04-01
  • OpenCVESSVC decisionpoc—
  • CNACVSS 3.15.3read 2026-10-23
  • CNAweakness (CWE)CWE-130, CWE-20read 2026-10-23
  • FIRST EPSSEPSS score0.5 %2026-10-23
  • PoC-in-GitHubproof of concept1read 2026-10-23
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Published
2026-03-27
Last Modified
2026-06-17
NVD status
Analyzed

Frequently asked questions

What is 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.

Is CVE-2026-33936 actively exploited?

A proof-of-concept exploit exists for CVE-2026-33936, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-33936?

CVE-2026-33936 has a CVSS v3 base score of 5.3 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

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