sigstore fulcio up to 1.8.2 OpenID Connect amplification

Summaryinfo

A vulnerability described as critical has been identified in sigstore fulcio up to 1.8.2. This affects an unknown part of the component OpenID Connect. Executing a manipulation can lead to amplification. This vulnerability is tracked as CVE-2025-66506. The attack can be launched remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in sigstore fulcio up to 1.8.2. It has been declared as critical. This vulnerability affects an unknown code block of the component OpenID Connect. The manipulation with an unknown input leads to a amplification vulnerability. The CWE definition for the vulnerability is CWE-405. The product does not properly control situations in which an adversary can cause the product to consume or produce excessive resources without requiring the adversary to invest equivalent work or otherwise prove authorization, i.e., the adversary's influence is "asymmetric." As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability was named CVE-2025-66506 since 12/03/2025. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

The vulnerability scanner Nessus provides a plugin with the ID 281772 (Amazon Linux 2 : runfinch-finch, --advisory ALAS2DOCKER-2025-092 (ALASDOCKER-2025-092)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 1.8.3 eliminates this vulnerability. Applying the patch 765a0e57608b9ef390e1eeeea8595b9054c63a5a is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (281772) and CERT Bund (WID-SEC-2026-0199). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Affected

• Red Hat OpenShift

Productinfo

Vendor

• sigstore

Name

• fulcio

Version

• 1.8.0
• 1.8.1
• 1.8.2

License

• open-source

Website

• Product: https://github.com/sigstore/fulcio/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Discussion