Skip to content
Fencer Vulns
critical 9.8

CVE-2026-33228 json

flatted: Prototype Pollution via parse()

published 2026-03-19 7 mo ago modified 2026-10-05 34 d ago also GHSA-rf6f-7fwh-wjgh , EUVD-2026-13881

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.9%
EPSS 0.9% chance of exploitation in 30 days, percentile 58%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm flatted 3.4.2
  • Red Hat Cluster Observability Operator 1.5.0 1782839279, 1782839996, 1782840539
  • Red Hat Red Hat Developer Hub 1.8 1776784286
  • Red Hat Red Hat Developer Hub 1.9 1777903262
  • node-flatted Debian 13 3.2.7~ds-1+deb13u1
  • node-flatted Debian 14 3.4.2~ds-1

debian advisories DEBIAN-CVE-2026-33228

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-33228 updated cvss 9.8

flatted: Flatted: Prototype pollution vulnerability allows arbitrary code execution via crafted JSON.

  • Red Hat 3scale API Management Platform 2 3scale-amp20/system, 3scale-amp21/system, 3scale-amp22/system, 3scale-amp24/system, 3scale-amp25/system, 3scale-amp26/system, +3 more Red Hat Build of Keycloak rhbk-quarkus-dist.zip Red Hat Single Sign-On 7 org.keycloak-keycloak-parent
    affected: no fix planned “Will not fix”
  • Red Hat Cluster Observability Operator 1.5 cluster-observability-operator/logging-console-plugin-pf4-rhel9 1782839279, cluster-observability-operator/logging-console-plugin-pf5-rhel9 1782840539, cluster-observability-operator/troubleshooting-panel-console-plugin-pf6-rhel9 1782839996
    fixed: vendor fix RHSA-2026:34342
  • Red Hat Ceph Storage 9.2 rhceph/rhceph-9-rhel10 1790843527
    fixed: vendor fix RHSA-2026:86618
  • Red Hat Developer Hub 1.8 rhdh 1776784286
    fixed: vendor fix RHSA-2026:9742
  • Red Hat Developer Hub 1.9 rhdh 1777903262
    fixed: vendor fix RHSA-2026:13826
  • Red Hat Cluster Observability Operator 1.5 cluster-observability-operator/perses-rhel9 1782839109, cluster-observability-operator/thanos-rhel9 1782840280, cluster-observability-operator/korrel8r-rhel9 1782839157, cluster-observability-operator/prometheus-rhel9 1782840780, cluster-observability-operator/alertmanager-rhel9 1782840761, cluster-observability-operator/perses-rhel9-operator 1782839191, +16 more
    not affected: vulnerable code not present
  • Red Hat Cryostat 4 io.cryostat-cryostat Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/kibana6-rhel8, openshift-logging/elasticsearch6-rhel9, openshift-logging/logging-curator5-rhel9, openshift-logging/elasticsearch-proxy-rhel9, openshift-logging/elasticsearch-rhel9-operator, openshift-logging/elasticsearch-operator-bundle Red Hat Multicluster Engine for Kubernetes multicluster-engine/console-mce-rhel9 Red Hat Advanced Cluster Management for Kubernetes 2 rhacm2/console-rhel9
    not affected: component not present
  • Red Hat AMQ Broker 7 org.jolokia-jolokia-parent
    not affected: vulnerable code not present
show 10 more
  • Red Hat build of Apicurio Registry 2 io.apicurio-apicurio-registry
    not affected: component not present
  • Red Hat build of OptaPlanner 8 org.optaweb.vehiclerouting-optaweb-vehicle-routing Red Hat Build of Podman Desktop podman-desktop-macos-1-0, podman-desktop-windows-1-0 Red Hat Ceph Storage 9.2 rhceph/alloy-rhel10 1790774976, rhceph/grafana-rhel10 1790774121, rhceph/keepalived-rhel10 1790842990, rhceph/oauth2-proxy-rhel10 1790774021, rhceph/snmp-notifier-rhel10 1790773439, rhceph/rhceph-haproxy-rhel10 1790846345
    not affected: vulnerable code not present
  • Red Hat Data Grid 8 org.infinispan-infinispan-console
    not affected: vulnerable code cannot be controlled by adversary
  • Red Hat Developer Hub 1.8 rhdh 1776783947, rhdh 1776787729 Red Hat Developer Hub 1.9 rhdh 1777902709, rhdh 1777909942 Red Hat Directory Server 11 389-ds-base Red Hat Directory Server 12 389-ds-base Red Hat Directory Server 13 389-ds-base
    not affected: vulnerable code not present
  • Red Hat Enterprise Linux 8 pcs, grafana, pcs-snmp, grafana-loki, grafana-mssql, grafana-mysql, +10 more Red Hat Enterprise Linux 9 pcs, rust, cargo, clippy, grafana, rustfmt, +12 more Red Hat Enterprise Linux 10 rust
    not affected: vulnerable code not in execute path
  • Red Hat Fuse 7 io.syndesis-syndesis-parent Red Hat JBoss Enterprise Application Platform 7 org.jboss.hal-hal-parent Red Hat JBoss Enterprise Application Platform 8 org.keycloak-keycloak-parent Red Hat JBoss Enterprise Application Platform Expansion Pack org.keycloak-keycloak-parent
    not affected: vulnerable code not present
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-mlflow-rhel9, rhoai/odh-dashboard-rhel8 Red Hat OpenShift Container Platform 4 openshift4/ose-console, openshift4/ose-console-rhel9 Red Hat Process Automation 7 org.uberfire-uberfire-parent, org.kie.workbench-kie-wb-common, org.kie-process-migration-service
    not affected: component not present
  • Red Hat Quay 3 quay/quay-rhel8, quay/quay-rhel9
    not affected: vulnerable code not present
  • Red Hat streams for Apache Kafka 2 com.github.streamshub-console
    not affected: vulnerable code not in execute path
  • Red Hat streams for Apache Kafka 3 com.github.streamshub-console
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
total
Assessed
7 mo ago

Exploit prediction

0.86% chance of exploitation in the next 30 days, higher than 58% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 8.9 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
CISA ADP 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 4.0 8.9 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
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
npm flatted
<3.4.2
3.4.2

Affected products

  • WebReflection flatted
  • Red Hat Cluster Observability Operator 1.5.0
  • Red Hat Red Hat Developer Hub 1.8
  • Red Hat Red Hat Developer Hub 1.9
  • Red Hat Cryostat 4
  • Red Hat Logging Subsystem for Red Hat OpenShift
  • Red Hat Multicluster Engine for Kubernetes
  • Red Hat Red Hat 3scale API Management Platform 2
  • Red Hat Red Hat Advanced Cluster Management for Kubernetes 2
  • Red Hat Red Hat AMQ Broker 7
  • Red Hat Red Hat build of Apicurio Registry 2
  • Red Hat Red Hat Build of Keycloak
  • Red Hat Red Hat build of OptaPlanner 8
  • Red Hat Red Hat Build of Podman Desktop
  • Red Hat Red Hat Data Grid 8
  • Red Hat Red Hat Directory Server 11
  • Red Hat Red Hat Directory Server 12
  • Red Hat Red Hat Directory Server 13
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat Fuse 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 8
  • Red Hat Red Hat JBoss Enterprise Application Platform Expansion Pack
  • Red Hat Red Hat OpenShift AI (RHOAI)
  • Red Hat Red Hat OpenShift Container Platform 4
  • Red Hat Red Hat Process Automation 7
  • Red Hat Red Hat Quay 3
  • Red Hat Red Hat Single Sign-On 7
  • Red Hat streams for Apache Kafka 2
  • Red Hat streams for Apache Kafka 3

Classification

Weakness
  • CWE-1321 Improperly Controlled Modification of Object Prototype Attributes
  • CWE-915 Improperly Controlled Modification of Dynamically-Determined Object Attributes

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.