CVE-2026-33228: WebReflection flatted prototype pollution in parse function

CVE-2026-33228 · Severity: critical · CVSS 9.8 · Published 2026-03-20

Flatted is a software library used to process complex data structures in JavaScript applications. A security flaw allows an attacker to send specially crafted data that can corrupt the application's internal memory. This can lead to a complete system takeover, data theft, or a total service outage.

Technologies: Red Hat build of Keycloak, Red Hat Developer Hub. Vendors: npm, Red Hat.

Quick answers

Is CVE-2026-33228 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-33228 being exploited in the wild.
How severe is CVE-2026-33228?
Critical severity, with a CVSS score of 9.8, published 20 March 2026.
Which products and versions are affected?
flatted (npm) <= 3.4.1, SEMVER:introduced=0,fixed=3.4.2.
Is there a fix for CVE-2026-33228?
Yes. flatted (npm): upgrade to 3.4.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-33228 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-33228?
Check whether you run flatted (npm), Red Hat build of Keycloak or Red Hat Developer Hub at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • flatted (npm): upgrade to 3.4.2 or later
    npm install flatted@3.4.2

Technical details

A prototype pollution vulnerability exists in the parse() function of the flatted library due to improper validation of array index keys. The parser uses attacker-controlled string values from the input JSON as direct keys for an internal JavaScript Array buffer. By providing the key '__proto__', an attacker can obtain a live reference to Array.prototype. Subsequent operations that write to properties of the parsed object can then modify the global prototype chain. This can be exploited remotely without authentication to achieve arbitrary code execution or denial of service. The issue is fixed in version 3.4.2 by ensuring index keys are validated as numeric and within bounds.

Affected products

  • WebReflection flatted <= 3.4.1
  • Red Hat Red Hat Developer Hub 1.8
  • Red Hat Red Hat Developer Hub 1.9
  • Red Hat Red Hat 3scale API Management Platform 2
  • Red Hat Red Hat Build of Keycloak
  • Red Hat Red Hat Single Sign-On 7

Identifiers

  • CVE-2026-33228
  • GHSA-rf6f-7fwh-wjgh

Timeline

  • 2026-03-17: patched: Version 3.4.2 released
  • 2026-03-19: advisory: GitHub Security Advisory GHSA-rf6f-7fwh-wjgh published
  • 2026-03-20: disclosed: CVE-2026-33228 published to NVD

References

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