CVE-2026-71553: ApostropheCMS Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-vmg4-6gfg-83qx
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CWE-1321
Published
Advisory Summary

CVE-2026-71553 is a HIGH denial of service vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting ApostropheCMS libraries in the npm ecosystem. The issue involves 2nd-order prototype pollution via patch leading to single-request persistent dos. Remediation is available in the latest vendor maintenance releases.

CVE-2026-71553 at a Glance

CVE Identifier CVE-2026-71553
GHSA Identifier GHSA-vmg4-6gfg-83qx
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Product ApostropheCMS
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-71553

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

apostrophe fixed: Latest secure release 
npm install apostrophe@Latest secure release
Verify Direct and Transitive Dependencies

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

npm ls apostrophe

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-71553, inspect your project dependencies using npm:

npm ls apostrophe

Analyze the terminal output to locate any version of ApostropheCMS in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The npm ls apostrophe command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution'), where the product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. In ApostropheCMS, 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

The vulnerability is a single-request persistent DoS by submitting e.g. "PATCH /api/v1/article/<id>" with a valid editor session and body of {"toString.call":"x"}, overwriting the global toString function with value x. Fabian

CVE-2026-71553 Affected ApostropheCMS Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
apostrophe
npm/apostrophe
npm
≤ 4.32.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-vmg4-6gfg-83qx
NVD — CVE-2026-71553 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-71553
Security Fix Commit FIX COMMIT
https://github.com/apostrophecms/apostrophe/commit/5a3746aaed49761e171c2cbfe793267c959829fd
ApostropheCMS Source Repository REPOSITORY
https://github.com/apostrophecms/apostrophe

Frequently Asked Questions

What is CVE-2026-71553?
CVE-2026-71553 is a security vulnerability in ApostropheCMS involving 2nd-order prototype pollution via PATCH leading to single-request persistent DoS under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution').
Which ApostropheCMS versions are affected?
Affected versions include releases prior to current release patches across affected packages: apostrophe.
What version fixes CVE-2026-71553?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is apostrophe affected?
Yes, apostrophe is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What CWE is associated with CVE-2026-71553?
CVE-2026-71553 is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.).
How can I check npm dependencies for CVE-2026-71553?
Run the dependency tree command: 'npm ls apostrophe'. 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-vmg4-6gfg-83qx",
  "modified" : "2026-09-02T15:12:42Z",
  "published" : "2026-09-02T15:12:41Z",
  "aliases" : [ "CVE-2026-71553" ],
  "summary" : "ApostropheCMS: 2nd-order prototype pollution via PATCH leading to single-request persistent DoS",
  "details" : "The vulnerability is a single-request persistent DoS by submitting e.g.\n\"PATCH /api/v1/article/<id>\" with a valid editor session and body of\n{\"toString.call\":\"x\"}, overwriting the global toString function with\nvalue x.\n\nFabian",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "apostrophe"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "4.32.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-vmg4-6gfg-83qx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-71553"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/apostrophecms/apostrophe/commit/5a3746aaed49761e171c2cbfe793267c959829fd"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/apostrophecms/apostrophe"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-02T15:12:41Z",
    "nvd_published_at" : "2026-08-17T20:16:46Z"
  }
}