CVE-2025-66506: Github.com/sigstore/fulcio Fulcio Allocates Excessive Memory During Vulnerability

HIGH
Advisory Identifier: GHSA-f83f-xpx7-ffpw
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CVSS 7.5
CWE-405
Published
Advisory Summary

CVE-2025-66506 is a HIGH (CVSS 7.5) fulcio allocates excessive memory during vulnerability (CWE-405: Asymmetric Resource Consumption (Amplification)) affecting Github.com/sigstore/fulcio libraries in the Go ecosystem. The issue involves fulcio allocates excessive memory during token parsing. Remediation is available by upgrading affected packages to version 1.8.3.

CVE-2025-66506 at a Glance

CVE Identifier CVE-2025-66506
GHSA Identifier GHSA-f83f-xpx7-ffpw
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-405: Asymmetric Resource Consumption (Amplification)
Affected Product Github.com/sigstore/fulcio
Package Ecosystem Go
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2025-66506

To remediate this vulnerability, upgrade all affected Github.com/sigstore/fulcio dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/sigstore/fulcio fixed: 1.8.3 
Upgrade github.com/sigstore/fulcio to 1.8.3
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/sigstore/fulcio

How to Check if You Are Affected

To determine whether your application is affected by CVE-2025-66506, inspect your project dependencies for Github.com/sigstore/fulcio:

inspect dependencies for github.com/sigstore/fulcio

Analyze the terminal output to locate any version of Github.com/sigstore/fulcio in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.8.3), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-405: Asymmetric Resource Consumption (Amplification), where 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.". In Github.com/sigstore/fulcio, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Function [identity.extractIssuerURL](https://github.com/sigstore/fulcio/blob/main/pkg/identity/issuerpool.go#L44-L45) currently splits (via a call to [strings.Split](https://pkg.go.dev/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. Relevant weakness: [CWE-405: Asymmetric Resource Consumption (Amplification)](https://cwe.mitre.org/data/definitions/405.html) Details See [identity.extractIssuerURL](https://github.com/sigstore/fulcio/blob/main/pkg/identity/issuerpool.go#L44-L45) Impact Excessive memory allocation

CVE-2025-66506 Affected Github.com/sigstore/fulcio Versions

1 component(s)
Fixed Versions:
1.8.3
Product / Package Ecosystem Affected Versions Fixed Version
github.com/sigstore/fulcio
golang/github.com/sigstore/fulcio
Go
< 1.8.3
1.8.3

References

GitHub Advisory / Wiki ADVISORY
https://github.com/sigstore/fulcio/security/advisories/GHSA-f83f-xpx7-ffpw
NVD — CVE-2025-66506 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-66506
Security Fix Commit FIX COMMIT
https://github.com/sigstore/fulcio/commit/765a0e57608b9ef390e1eeeea8595b9054c63a5a
Github.com/sigstore/fulcio Source Repository REPOSITORY
https://github.com/sigstore/fulcio

Frequently Asked Questions

What is CVE-2025-66506?
CVE-2025-66506 is a security vulnerability in Github.com/sigstore/fulcio involving Fulcio allocates excessive memory during token parsing under CWE-405: Asymmetric Resource Consumption (Amplification).
Which Github.com/sigstore/fulcio versions are affected?
Affected versions include releases prior to 1.8.3 across affected packages: github.com/sigstore/fulcio.
What version fixes CVE-2025-66506?
Upgrading to 1.8.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/sigstore/fulcio affected?
Yes, github.com/sigstore/fulcio is affected in releases prior to 1.8.3. Upgrade your dependency to 1.8.3 or later.
What is the CVSS score of CVE-2025-66506?
CVE-2025-66506 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2025-66506?
CVE-2025-66506 is classified under CWE-405: Asymmetric Resource Consumption (Amplification) (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.").
How can I check Go dependencies for CVE-2025-66506?
Run the dependency tree command: 'inspect dependencies for github.com/sigstore/fulcio'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f83f-xpx7-ffpw",
  "modified" : "2025-12-05T18:18:26Z",
  "published" : "2025-12-05T18:18:26Z",
  "aliases" : [ "CVE-2025-66506" ],
  "summary" : "Fulcio allocates excessive memory during token parsing",
  "details" : "Function [identity.extractIssuerURL](https://github.com/sigstore/fulcio/blob/main/pkg/identity/issuerpool.go#L44-L45) currently splits (via a call to [strings.Split](https://pkg.go.dev/strings#Split)) its argument (which is untrusted data) on periods.\n\nAs 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. Relevant weakness: [CWE-405: Asymmetric Resource Consumption (Amplification)](https://cwe.mitre.org/data/definitions/405.html)\n\nDetails\nSee [identity.extractIssuerURL](https://github.com/sigstore/fulcio/blob/main/pkg/identity/issuerpool.go#L44-L45)\n\nImpact\nExcessive memory allocation",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/sigstore/fulcio"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.8.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.8.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sigstore/fulcio/security/advisories/GHSA-f83f-xpx7-ffpw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-66506"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sigstore/fulcio/commit/765a0e57608b9ef390e1eeeea8595b9054c63a5a"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sigstore/fulcio"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-405" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-12-05T18:18:26Z",
    "nvd_published_at" : "2025-12-04T22:15:49Z"
  }
}