# CVE-2025-66506

## Summary

- **CVE ID:** CVE-2025-66506
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
- **CWE:** CWE-405
- **Published:** Dec 4, 2025
- **Last Modified:** Mar 13, 2026

## 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.

## Affected Products

- sigstore — fulcio (< 1.8.3)

## References

- [CNA](https://github.com/sigstore/fulcio/security/advisories/GHSA-f83f-xpx7-ffpw)
- [CNA](https://github.com/sigstore/fulcio/commit/765a0e57608b9ef390e1eeeea8595b9054c63a5a)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.21%
- **EPSS Percentile:** 11.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-12._