CVE-2026-33228 — Security Box Score

CVE · referencelatest edition

Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-33228HIGH

WebReflection flatted — flatted: Prototype Pollution via parse()

  AV  AC  AT  PR  UI  VC  VI  VA   CVSS    EPSS   %ile   KEV
   N   L   N   N   N   H   H   H    8.9   .0081   54.0     —

AFFECTED
  Product  Versions   Fixed
  flatted  < 3.4.2 –  —

TIMELINE
  Mar 18  Reserved by GitHub_M
  Mar 20  Published (CNA: GitHub_M)
  Aug 4   EXPLOIT PUBLISHED — CVE-2026-33228 (WebReflection flatted). Public exploit reference added.

CWE-1321 · CNA: GitHub_M · CVSS v4.0 · 9 references · NVD status: Modified

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.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
March 18, 2026	Reserved	Reserved by GitHub_M
March 20, 2026	Published	Published (CNA: GitHub_M)
August 4, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-33228 (WebReflection flatted). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
WebReflection	flatted	—	< 3.4.2	—

Weaknesses

CWE-1321

References (9)

https://access.redhat.com/errata/RHSA-2026:13826 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/errata/RHSA-2026:34342 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/errata/RHSA-2026:9742 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/security/cve/CVE-2026-33228 [vdb-entry, x_refsource_REDHAT]
https://bugzilla.redhat.com/show_bug.cgi?id=2449872 [issue-tracking, x_refsource_REDHAT]
https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802 [x_refsource_MISC]
https://github.com/WebReflection/flatted/releases/tag/v3.4.2 [x_refsource_MISC]
https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh [x_refsource_CONFIRM]
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33228.json [x_sadp-csaf-vex]

Authoritative record: CVE-2026-33228 at cve.org

Vendors: webreflection

Weaknesses: CWE-1321

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-33228 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.