{"id":"CVE-2026-33936","aliases":["GHSA-9f5j-8jwj-x28g","PYSEC-2026-2467"],"url":"https://o3.security/vulnerability/CVE-2026-33936","summary":"python-ecdsa: Denial of Service via improper DER length validation in crafted private keys","details":"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.","published":"2026-03-27T22:08:22.868Z","modified":"2026-08-12T03:51:31.831528189Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":{"score":0.00476,"percentile":0.40112,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"ecdsa","fixedVersion":"0.19.2"}],"fix":{"url":"https://github.com/tlsfuzzer/python-ecdsa/commit/bd66899550d7185939bf27b75713a2ac9325a9d3","label":"tlsfuzzer/python-ecdsa@bd66899"},"references":[{"type":"WEB","url":"https://github.com/tlsfuzzer/python-ecdsa/releases/tag/python-ecdsa-0.19.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33936.json"},{"type":"ADVISORY","url":"https://github.com/tlsfuzzer/python-ecdsa/security/advisories/GHSA-9f5j-8jwj-x28g"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33936"},{"type":"FIX","url":"https://github.com/tlsfuzzer/python-ecdsa/commit/bd66899550d7185939bf27b75713a2ac9325a9d3"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:31.831528189Z"}}