Vulnerability · Published Dec 4, 2025 · Assigned by GitHub_M
CVE-2025-66506Fulcio allocates excessive memory during token parsing
High 7.5
In plain English
A high-severity security flaw in fulcio from sigstore. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | golang-github-sigstore-fulcio | no fix listed | DEBIAN-CVE-2025-66506 |
| Debian:14 | golang-github-sigstore-fulcio | 1.8.5-1 | DEBIAN-CVE-2025-66506 |
| Go | github.com/sigstore/fulcio | 1.8.3 | GO-2025-4193 |
| Go | github.com/sigstore/fulcio | 1.8.3 | GHSA-f83f-xpx7-ffpw |
| Ubuntu:25.10 | golang-github-sigstore-fulcio | no fix listed | UBUNTU-CVE-2025-66506 |
| Ubuntu:26.04:LTS | golang-github-sigstore-fulcio | no fix listed | UBUNTU-CVE-2025-66506 |
| Ubuntu:26.10 | golang-github-sigstore-fulcio | no fix listed | UBUNTU-CVE-2025-66506 |
Affected products (as reported)
Weakness: CWE-405 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H