Parsing Vulnerability in Fulcio Certificate Authority from Sigstore
CVE-2025-66506

7.5HIGH

Key Information:

Vendor

Sigstore

Status
Fulcio
Vendor
CVE Published:
4 December 2025

What is CVE-2025-66506?

Fulcio, the certificate authority from Sigstore for issuing code signing certificates, is susceptible to a data parsing issue in versions prior to 1.8.3. Specifically, the vulnerability arises in the function identity.extractIssuerURL, which improperly handles untrusted data by naively splitting input strings on periods. This can lead to problematic allocations where the system may experience excessive memory usage in response to crafted requests containing malicious OIDC identity tokens. Such tokens can include numerous period characters, posing a risk of resource exhaustion. This issue has been rectified in version 1.8.3.

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Affected Version(s)

fulcio < 1.8.3

References

https://github.com/sigstore/fulcio/security/advisories/GH...
x_refsource_CONFIRM
https://github.com/sigstore/fulcio/commit/765a0e57608b9ef...
x_refsource_MISC

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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