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CVE-2026-33228

Webreflection Flatted vulnerability

9.8 CRITICALPublic exploitEPSS 0.99%
  1. Published20 Mar 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Webreflection Flatted< 3.4.2

Remediation

Fixed in
Webreflection Flatted≥ 3.4.2

References

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Frequently asked

Is CVE-2026-33228 being actively exploited?

CVE-2026-33228 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.99%.

How severe is CVE-2026-33228?

CVE-2026-33228 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.99% probability of exploitation.

Which products are affected by CVE-2026-33228?

Affected products include Webreflection Flatted.

How do I fix CVE-2026-33228?

Upgrade affected software to a fixed version, for example Webreflection Flatted 3.4.2 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-33228 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.