CVE-2025-64076Public exploitNetwork attack vector

Denial of service via decoder boundary errors

Published Nov 18, 2025 · Updated Nov 19, 2025

Denial of service in cbor2 before 5.7.1 allows remote attackers to crash processes or exhaust memory via crafted CBOR text strings. decode_definite_long_string() retains a stale buffer length after consuming split UTF-8 bytes, computes a negative chunk size for read(), and leaks each chunk reference. Exposure requires the C extension to decode untrusted definite-length text strings spanning 65,536-byte boundaries; pure-Python decoding is outside the reported flaw.

CVSS severity7.5
High
EPSS probability0.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in cbor2 before 5.7.1 allows remote attackers to crash processes or exhaust memory via crafted CBOR text strings. decode_definite_long_string() retains a stale buffer length after consuming split UTF-8 bytes, computes a negative chunk size for read(), and leaks each chunk reference. Exposure requires the C extension to decode untrusted definite-length text strings spanning 65,536-byte boundaries; pure-Python decoding is outside the reported flaw.

The record

CVE
CVE-2025-64076
Published
Nov 18, 2025
Updated
Nov 19, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-191, CWE-401, CWE-125, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 18, 2025CVE publishedPublication date reported by the CVE source.
  2. Nov 19, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5MITRECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-191Integer Underflow (Wrap or Wraparound)
CWE-401Missing Release of Memory after Effective Lifetime
CWE-125Out-of-bounds Read
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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