Insufficient verification of data authenticity in Fulcio - #VU132352
Published: May 27, 2026
Vulnerability identifier: #VU132352
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: N/A
CWE-ID: CWE-345
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Sigstore
Affected software:
Fulcio
Fulcio
Detailed vulnerability description
The vulnerability allows a remote attacker to bypass signature verification integrity checks.
The vulnerability exists due to improper restriction of cross-host redirects in the OIDC discovery flow and verifier cache when processing a malicious jwks_uri. A remote attacker can return discovery metadata that points jwks_uri to an attacker-controlled host to bypass signature verification integrity checks.
The issue can poison the verifier cache with attacker-controlled verification keys.
Remediation
Install security update from vendor's website.