Description
pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.5, binary REAL decoding builds a large mantissa one octet at a time by shifting a growing integer and slicing the remaining byte string. Attacker-controlled ASN.1 includes a binary-encoded REAL with a large mantissa and reaches BER, CER, or DER decode(), with or without a schema containing REAL. RealPayloadDecoder.valueDecoder repeatedly performs a left shift, OR, and suffix copy for every mantissa octet, making decode time quadratic in mantissa length. A comparatively small REAL value can hold a decoding worker on one CPU core for seconds or longer and cause availability loss. This issue is fixed in version 0.6.5.
Published: 2026-10-29
Score: 7.5 High
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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History

Thu, 29 Oct 2026 20:00:00 +0000

Type Values Removed Values Added
Description pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.5, binary REAL decoding builds a large mantissa one octet at a time by shifting a growing integer and slicing the remaining byte string. Attacker-controlled ASN.1 includes a binary-encoded REAL with a large mantissa and reaches BER, CER, or DER decode(), with or without a schema containing REAL. RealPayloadDecoder.valueDecoder repeatedly performs a left shift, OR, and suffix copy for every mantissa octet, making decode time quadratic in mantissa length. A comparatively small REAL value can hold a decoding worker on one CPU core for seconds or longer and cause availability loss. This issue is fixed in version 0.6.5.
Title pyasn1: Quadratic-complexity denial of service in binary REAL decoding
Weaknesses CWE-407
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


Subscriptions

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-10-29T19:48:52.470Z

Reserved: 2026-10-29T16:04:48.728Z

Link: CVE-2026-119197

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-29T20:17:30.907

Modified: 2026-10-29T20:17:30.907

Link: CVE-2026-119197

cve-icon Redhat

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cve-icon OpenCVE Enrichment

No data.

Weaknesses
  • CWE-407

    Inefficient Algorithmic Complexity