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CVE-2026-33228

9.8 · CRITICAL

flatted is a circular JSON parser.

Published Mar 20, 2026CWE-1321EPSS 1.28%

Overview

CVE-2026-33228 is a critical-severity vulnerability. It was published on March 20, 2026 and has a CVSS 3.1 base score of 9.8 (CRITICAL).

This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

flatted is a circular JSON parser. Prior to version 3.4.2, the parse() function in flatted can use attacker-controlled string values from the parsed JSON as direct array index keys, without validating that they are numeric. Since the internal input buffer is a JavaScript Array, accessing it with the key "__proto__" returns Array.prototype via the inherited getter. This object is then treated as a legitimate parsed value and assigned as a property of the output object, effectively leaking a live reference to Array.prototype to the consumer. Any code that subsequently writes to that property will pollute the global prototype. This issue has been patched in version 3.4.2.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802GitHubgithub.com/WebReflection/flatted/releases/tag/v3.4.2GitHubgithub.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjghRefaccess.redhat.com/errata/RHSA-2026:13826Refaccess.redhat.com/errata/RHSA-2026:34342Refaccess.redhat.com/errata/RHSA-2026:9742Refaccess.redhat.com/security/cve/CVE-2026-33228Refbugzilla.redhat.com/show_bug.cgi?id=2449872Refsecurity.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33228.json

How CyberStrike helps

Frequently asked questions

What is CVE-2026-33228?

CVE-2026-33228 is a critical-severity vulnerability. It was published on March 20, 2026 and has a CVSS 3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-33228?

This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-33228?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-33228?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-33228 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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