CVE-2026-75866Network attack vector

Authorization bypass via unchecked token scope

Published Aug 22, 2026 · Updated Aug 22, 2026

Missing authorization in Punk::OAuth2::Server 0.03 and earlier allows remote attackers to obtain over-scoped signed access tokens. The token path accepts the request-body grant_type and requested scope without comparing either value with the client registration, while authorize stores an unchecked query scope in authorization codes. Exploitation requires a registered client identifier; secretless clients need no additional credential, and Punk::OAuth2::Checker honors the resulting token scope.

CVSS severity9.1
Critical
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Missing authorization in Punk::OAuth2::Server 0.03 and earlier allows remote attackers to obtain over-scoped signed access tokens. The token path accepts the request-body grant_type and requested scope without comparing either value with the client registration, while authorize stores an unchecked query scope in authorization codes. Exploitation requires a registered client identifier; secretless clients need no additional credential, and Punk::OAuth2::Checker honors the resulting token scope.

The record

CVE
CVE-2026-75866
Published
Aug 22, 2026
Updated
Aug 22, 2026
Vendor
Robert Acock
Product
Punk::OAuth2
Classifications
CWE-862, T1550.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 22, 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.

  1. Affected versionversion=0 <=0.03

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Robert Acock · Punk::OAuth2version=0 <=0.03

Published CVSS scores

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-862Missing Authorization
T1550.001Use Alternate Authentication Material: Application Access Token

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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