CVE-2026-33228

HIGH EPSS 48.7%
Published Mar 20, 20263mo ago · Modified Jun 27, 20266d ago
8.9 CVSS 4.0
High
Find Similar
Published Mar 20, 2026 3mo ago
Last Modified Jun 27, 2026 6d ago

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 Details

Base Score
8.9
Exploitability
—
Impact
—
Vector string
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
48.7% percentile
Exploit & Patch Status
Public Exploit Known
Patch Available

Weaknesses 2

CWE-1321
CWE-915

Affected Products 1

VendorProductVersionRange
webreflectionflatted* <3.4.2

References 8

  • access.redhat.com https://access.redhat.com/errata/RHSA-2026:13826
  • access.redhat.com https://access.redhat.com/errata/RHSA-2026:9742
  • access.redhat.com https://access.redhat.com/security/cve/CVE-2026-33228
  • bugzilla.redhat.com https://bugzilla.redhat.com/show_bug.cgi?id=2449872
  • github.com https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802
    Patch
  • github.com https://github.com/WebReflection/flatted/releases/tag/v3.4.2
    Product
  • github.com https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh
    ExploitVendor Advisory
  • security.access.redhat.com https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33228.json

Remediation

  • github.com https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802
    Patch