CVE-2026-33936— python-ecdsa: Denial of Service via improper DER length validation in crafted private keys
Quick assessment
Affected
tlsfuzzer python-ecdsa
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Pure-Python ECDSA and ECDH是tlsfuzzer开源的一个纯Python实现的椭圆曲线密码学库。 Pure-Python ECDSA and ECDH 0.19.2之前版本存在安全漏洞，该漏洞源于低级DER解析函数问题，可能导致解析恶意DER私钥时引发意外异常，造成应用程序崩溃和拒绝服务。
Possible ATT&CK Techniques 1 AI
T1496 · Resource Hijacking
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I. Basic Information for CVE-2026-33936
Vulnerability Information
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Vulnerability Title
python-ecdsa: Denial of Service via improper DER length validation in crafted private keys
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
输入验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Pure-Python ECDSA and ECDH 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Pure-Python ECDSA and ECDH是tlsfuzzer开源的一个纯Python实现的椭圆曲线密码学库。 Pure-Python ECDSA and ECDH 0.19.2之前版本存在安全漏洞，该漏洞源于低级DER解析函数问题，可能导致解析恶意DER私钥时引发意外异常，造成应用程序崩溃和拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| tlsfuzzer | python-ecdsa | < 0.19.2 | - |
|
II. Public POCs for CVE-2026-33936
| # | POC Description | Source Link | Shenlong Link |
|---|
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Patches & Fixes for CVE-2026-33936 (2)
-
Release 0.19.2 · tlsfuzzer/python-ecdsa · GitHub x_refsource_MISC
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Merge commit from fork · tlsfuzzer/python-ecdsa@bd66899 · GitHub x_refsource_MISC
Vendor Advisories for CVE-2026-33936 (1)
IV. Related Vulnerabilities
V. Comments for CVE-2026-33936
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