PT-2026-26465 · Flatted · Flatted

Yohannslm · Published 2026-03-19 · Updated 2026-05-08 · CVE-2026-33228

Positive Technologies (AI Summary)

CVSS v3.1

9.8

Critical

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Name of the Vulnerable Software and Affected Versions flatted versions prior to 3.4.2

Description flatted is a circular JSON parser. The parse() function does not validate that string values from the parsed JSON used as array index keys are numeric. This allows attacker-controlled strings, such as " proto ", to be used as keys, accessing Array.prototype via the inherited getter. This prototype is then treated as a parsed value and assigned to the output object, leaking a live reference to Array.prototype to the consumer. Subsequent writes to this property can pollute the global prototype chain. The issue resides in the esm/index.js file, specifically within the resolver function, where the input array is accessed using a potentially unsafe key value. The vulnerable code does not ensure that value is a valid numeric index before accessing the input array. This can lead to denial of service or code execution.

Recommendations versions prior to 3.4.2: Upgrade to version 3.4.2 or later to resolve this issue.

Exploit

Fix

Prototype Pollution

Weakness Enumeration

CWE-1321

Related Identifiers

CVE-2026-33228

GHSA-RF6F-7FWH-WJGH

Affected Products

Flatted

References · 16

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33228.json · Exploit
• https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802 · Patch
• https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh · Vendor Advisory
• https://osv.dev/vulnerability/GHSA-rf6f-7fwh-wjgh · Vendor Advisory
• https://security-tracker.debian.org/tracker/CVE-2026-33228 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-33228 · Security Note
• https://ubuntu.com/security/CVE-2026-33228 · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2026-33228 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2026-33228 · Security Note
• https://osv.dev/vulnerability/UBUNTU-CVE-2026-33228 · Vendor Advisory
• https://osv.dev/vulnerability/DEBIAN-CVE-2026-33228 · Vendor Advisory
• https://osv.dev/vulnerability/ROOT-APP-NPM-CVE-2026-33228 · Vendor Advisory
• https://github.com/WebReflection/flatted/releases/tag/v3.4.2 · Note
• https://github.com/WebReflection/flatted · Note
• https://twitter.com/TheHackerWire/status/2036186170045186353 · Twitter Post