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.
CVE-2026-33228
CRITICALCVSS 9.89.8Elevated
EchelonGraph scoreLOW confidence
This critical-severity CVE scores 9.8 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: adp:redhat-sadp
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 9.8Exploit: NoneExposed: 0
A fix is available — apply it.
- CVSS v3
- 9.8
- EG Score
- 9.8(low)
- EPSS
- 52.4%
- KEV
- Not listed
Published
March 20, 2026
Last Modified
July 3, 2026
Advisory Details (8)
Auto-updated Jul 3, 2026Patch available. Sources: github_commit, github, redhat.
redhat Patch Available
Affected: Red Hat Enterprise Linux 10",
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33228.jsonredhat Patch Available
2449872 – (CVE-2026-33228) CVE-2026-33228 flatted: Flatted: Prototype pollution vulnerability allows arbitrary code execution via crafted JSON.
https://bugzilla.redhat.com/show_bug.cgi?id=2449872redhat Patch Available
redhat Patch Available
redhat Patch Available
github Patch Available
Prototype Pollution via parse() in NodeJS flatted (CWE-1321) · Advisory · WebReflection/flatted · GitHub
https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjghgithub_commit
commit 885ddcc33cf9 (WebReflection/flatted)
Fix landed in WebReflection/flatted commit 885ddcc33cf9 — awaiting tagged release
https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802Vendor Advisories for CVE-2026-33228(4)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- RHSA-2026:34342Red Hat Product SecurityCritical
Red Hat Security Advisory: Cluster Observability Operator 1.5.0
- CVE-2026-33228Microsoft Security Response Center (MSRC)High
flatted: Prototype Pollution via parse()
- RHSA-2026:13826Red Hat Product SecurityCritical
Red Hat Security Advisory: Red Hat Developer Hub 1.9.4 release.
- RHSA-2026:9742Red Hat Product SecurityCritical
Red Hat Security Advisory: Red Hat Developer Hub 1.8.6 release.
Patch Availability(2)
| Vendor / Ecosystem | Fixed in / Patch | Released | Source |
|---|---|---|---|
| redhat | rhdh/rhdh-hub-rhel9:1777903262 | 2026-05-05 | redhat |
| redhat | rhdh/rhdh-hub-rhel9:1776784286 | 2026-04-22 | redhat |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(1 across 1 ecosystem)
npm(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| flatted | — | 3.4.2 | — |
Weakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 8× in last 7d / 15× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-06 16:27 UTCEPSS rescore
- 2026-07-06 16:27 UTCEPSS rescore
- 2026-07-06 02:23 UTCEPSS rescore
- 2026-07-06 02:23 UTCEPSS rescore
- 2026-07-05 02:30 UTCEPSS rescore
- 2026-07-04 06:31 UTCEPSS rescore
- 2026-07-01 15:06 UTCEPSS rescore
- 2026-06-30 23:22 UTCEPSS rescore
- 2026-06-28 14:07 UTCEPSS rescore
- 2026-06-28 14:07 UTCEPSS rescore
- 2026-06-28 04:56 UTCEPSS rescore
- 2026-06-28 04:56 UTCEPSS rescore
- 2026-06-27 05:23 UTCEG score recompute
- 2026-06-27 05:23 UTCVendor advisory
- 2026-06-27 05:22 UTCMITRE cvelistV5first tracked
Frequently asked(5)
What is CVE-2026-33228?
CVE-2026-33228 is a critical vulnerability published on March 20, 2026. 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…
When was CVE-2026-33228 disclosed?
CVE-2026-33228 was first published in the National Vulnerability Database on March 20, 2026, with the most recent update on July 3, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-33228 actively exploited?
CVE-2026-33228 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 52.4% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-33228?
CVE-2026-33228 has a CVSS v3 base score of 9.8 (NVD). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-33228?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-33228, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-33228
Is Your Infrastructure Affected by CVE-2026-33228?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.