ZDF
Sign inSign up

Vulnerabilities

Vulnerability · CVE-2026-33228

flatted is a circular JSON parser.

Published Mar 20, 2026 · catalog updated Sep 4, 2026 · Red Hat

Check if you run it

No confirmed exploitation is on record for CVE-2026-33228. EPSS is 1.28%. Act only if a listed version of Red Hat is installed.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Critical9.8
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
1.28%
Remediation
Advisory link
Affected products
cpe webreflection/flatted

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe webreflection/flattedversion unspecified

How to fix CVE-2026-33228

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-33228. EPSS is 1.28%. Act only if a listed version of Red Hat is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-1321: Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution); CWE-915: Improperly Controlled Modification of Dynamically-Determined Object Attributes. EPSS 1.28%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 20, 2026 · NIST NVD

    Detected

    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

  2. Sep 4, 2026 · NIST NVD

    Updated

    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

Sources

  • CSAF AdvisoriesVendor advisoryRHSA-2026:9742:CVE-2026-33228

    A flaw was found in flatted, a JavaScript Object Notation (JSON) parser designed for handling circular data structures. A remote attacker can exploit this vulnerability by providing specially crafted JSON input. The parse() function in flatted fails to properly validate string va

    security.access.redhat.com
  • CVE.orgVulnerability recordCVE-2026-33228

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-33228

    30-day exploitation probability 1.3%

    first.org
  • NIST NVDVulnerability recordCVE-2026-33228

    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, a

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.