CVE-2025-66506

HIGH

Fulcio < 1.8.3 - Denial of Service via OIDC Identity Token Period Character Amplification

Title source: llm
STIX 2.1

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.

References (2)

Core 2

Scores

CVSS v3 7.5
EPSS 0.0018
EPSS Percentile 8.1%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CISA SSVC

Vulnrichment
Exploitation none
Automatable yes
Technical Impact partial

Details

CWE
CWE-405
Status published
Products (2)
linuxfoundation/fulcio < 1.8.3
sigstore/fulcio 0 - 1.8.3Go
Published Dec 04, 2025
Tracked Since Feb 18, 2026