Denial of service via truncated DER length
Published Mar 27, 2026 · Updated Mar 27, 2026
Improper DER validation in python-ecdsa before 0.19.2 allows remote attackers to crash applications through malformed private keys. The ecdsa.der.remove_octet_string function trusts an OCTET STRING length that exceeds the remaining buffer, so SigningKey.from_der reaches an internal IndexError instead of rejecting the input. Exploitation requires an application to parse an attacker-controlled DER private key, and the bounded consequence is interruption of that application when the exception is unhandled.
Summary
What happened
Improper DER validation in python-ecdsa before 0.19.2 allows remote attackers to crash applications through malformed private keys. The ecdsa.der.remove_octet_string function trusts an OCTET STRING length that exceeds the remaining buffer, so SigningKey.from_der reaches an internal IndexError instead of rejecting the input. Exploitation requires an application to parse an attacker-controlled DER private key, and the bounded consequence is interruption of that application when the exception is unhandled.
The record
- CVE
- CVE-2026-33936
- Published
- Mar 27, 2026
- Updated
- Mar 27, 2026
- Vendor
- tlsfuzzer
- Product
- python-ecdsa
- Classifications
- CWE-130, CWE-20, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 27, 2026CVE publishedPublication date reported by the CVE source.
- Mar 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 0.19.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Malformed DER reproduction scriptsproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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