Home/CVE/Fulcio is a free-to-use certificate authority for issuing code signing certificates for an OpenID Connect (OIDC) identit
CVE

CVE-2025-66506

Fulcio is a free-to-use certificate authority for issuing code signing certificates for an OpenID Connect (OIDC) identit

Fulcio is a free-to-use certificate authority for issuing code signing certificates for an OpenID Connect (OIDC) identity. Prior to 1.8.3, function identity.extractIssuerURL splits (via a call to strings.Split) its argument (which is untrusted data) on periods. As a result, in the face of a malicious request with an (invalid) OIDC identity token in the payload containing many period characters, a call to extractIssuerURL incurs allocations to the tune of O(n) bytes (where n stands for the length of the function's argument), with a constant factor of about 16.

This vulnerability is fixed in 1.8.3.

HIGH · CVSS 7.5 EPSS 0.00043
Schedule remediation
  • SSVC automatable: yes - attacks can be scripted at scale
  • CVSS base score ≥ 7.0
Sigma rules0 YARA rules0
⬡

Weakness Classification

CWE-405Asymmetric Resource Consumption (Amplification)
▤

Affected Products & Versions

1
linuxfoundation fulcio< 1.8.3
▤

Affected Packages

1
Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
Go github.com/sigstore/fulcio HIGH fixed in 1.8.3
▣

Scoring & Timeline

7.5
HIGH · CVSS v3.1 · security-advisories@github.com
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD04 Dec 2025 · 10:15 PM
CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
yes
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

30
rhsaRHSA-2026:6170Important
rhsaRHSA-2026:6166Important
rhsaRHSA-2026:3462Important
rhsaRHSA-2026:3461Important
rhsaRHSA-2026:3713Important
🔗

References & Sources

2
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://github.com/sigstore/fulcio/commit/765a0e57608b9ef390e1eeeea8595b9054c63a5aPatch
https://github.com/sigstore/fulcio/security/advisories/GHSA-f83f-xpx7-ffpwVendor Advisory
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