CVE-2025-66506

Fulcio allocates excessive memory during token parsing

Published Dec 4, 2025 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-f83f-xpx7-ffpw Fulcio allocates excessive memory during token parsing
History
Type Values Removed Values Added
First Time appeared Linuxfoundation
Linuxfoundation fulcio
CPEs cpe:2.3:a:linuxfoundation:fulcio:*:*:*:*:*:*:*:*
Vendors & Products Linuxfoundation
Linuxfoundation fulcio
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Sigstore
Sigstore fulcio
Vendors & Products Sigstore
Sigstore fulcio
Type Values Removed Values Added
Description 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.
Title Fulcio allocates excessive memory during token parsing
Weaknesses CWE-405
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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Dec 5, 2025, 3:32 PM
Reserved
Dec 3, 2025, 3:12 PM
Status
Analyzed
Published
Dec 4, 2025, 10:15 PM
Modified
Oct 18, 2026, 3:10 PM
Severity
Important
Public date
Dec 4, 2025, 10:04 PM