CVE-2025-66506Network attack vector

Service interruption via unbounded token splitting

Published Dec 4, 2025 · Updated Dec 5, 2025

Resource exhaustion in Sigstore Fulcio before 1.8.3 allows remote attackers to interrupt the service via a malformed OIDC identity token. The identity.extractIssuerURL function uses strings.Split on the entire untrusted token before validating its three-part structure, allocating about 16 bytes per input byte when periods are abundant. No authentication or user interaction is required, and a sufficiently large request can exhaust memory and make the certificate-authority service unavailable.

CVSS severity7.5
High
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Sigstore Fulcio before 1.8.3 allows remote attackers to interrupt the service via a malformed OIDC identity token. The identity.extractIssuerURL function uses strings.Split on the entire untrusted token before validating its three-part structure, allocating about 16 bytes per input byte when periods are abundant. No authentication or user interaction is required, and a sufficiently large request can exhaust memory and make the certificate-authority service unavailable.

The record

CVE
CVE-2025-66506
Published
Dec 4, 2025
Updated
Dec 5, 2025
Vendor
Sigstore
Product
Fulcio
Classifications
CWE-405, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 4, 2025CVE publishedPublication date reported by the CVE source.
  2. Dec 5, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.8.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Sigstore · Fulcioversion=< 1.8.3

Published CVSS scores

7.5GitHub, Inc.CVSS: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 exploitUnconfirmed

Weakness, pattern, technique

CWE-405Asymmetric Resource Consumption (Amplification)
T1499.003Application Exhaustion Flood

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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