fast-xml-parser: Entity Expansion Limits Bypassed When Set to Zero Due to JavaScript Falsy Evaluation
NaturalIntelligence · fast-xml-parser
Official source article: GitHub GHSA-JP2Q-39XQ-3W4G ↗. Check the applicable product and release in the original source.
5.9MediumCVSS 3.1
Recommended action
Patch only the product branches with a verified fix
Medium technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 4 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Published severityMedium→Operational priority:High, raised one band.upgradedsince 25 Mar 2026
Evidence used
No CISA KEV confirmation is currently recorded.
A structured source references public exploit or proof-of-concept material.
The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
EPSS is 0.48% for the current model date.
Compensating controls
Validate the affected product branch and deploy the verified fixed release.
Restrict the affected network interface to trusted sources where business-safe.
Increase monitoring for the attack path and post-exploitation behaviour described in the report.
Verification
Confirm that the asset runs NaturalIntelligence fast-xml-parser and falls inside the recorded affected range.
Verify the installed build against the product-specific fixed version after deployment.
Validate exposure, authentication requirements and compensating controls in the actual environment.
Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Cross-source reconciliation
Remediation availability differs by product scope
Verified remediation exists for at least one product or source, but 4 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Debian Security Tracker: 4 affected package states with no published fix
Distribution package intelligence
Release-specific package status
Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.
5 package states
Package result overrides the generic status
BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 4 affected package states shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
Distribution release
Source package
Vendor state
Fixed version
Evidence
Debian trixietrixie · source
node-webfont
Affected, no fix publishedDebian currently tracks this release as open.
These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
1 current
CVE-2026-33349 · CSAF 2.0 · revision 3 · finalRed Hat Product Securityfast-xml-parser: fast-xml-parser: Denial of Service via unbounded entity expansion due to incorrect configuration limit handling
13 known affected
The vendor explicitly identifies these products as affected by this CVE.
mta/mta-ui-rhel9 as a component of Migration Toolkit for Applications 8
advanced-cluster-security/rhacs-main-rhel8 as a component of Red Hat Advanced Cluster Security 4
apicurio/apicurio-registry-ui-rhel8 as a component of Red Hat Data Grid 8
apicurio/apicurio-registry-ui-rhel9 as a component of Red Hat Data Grid 8
rhdh/backstage-community-plugin-catalog-backend-module-scaffolder-relation-processor as a component of Red Hat Developer Hub
rhoai/odh-mlflow-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
openshift-gitops-1/argocd-rhel8 as a component of Red Hat OpenShift GitOps
openshift-gitops-1/argocd-rhel9 as a component of Red Hat OpenShift GitOps
container-native-virtualization/kubevirt-console-plugin as a component of Red Hat OpenShift Virtualization 4
container-native-virtualization/kubevirt-console-plugin-rhel9 as a component of Red Hat OpenShift Virtualization 4
satellite/iop-host-inventory-frontend-rhel9 as a component of Red Hat Satellite 6
satellite/iop-vulnerability-frontend-rhel9 as a component of Red Hat Satellite 6
Summary
A flaw was found in fast-xml-parser. A remote attacker can exploit this vulnerability by providing specially crafted XML input to an application using the affected library. The DocTypeReader component incorrectly processes configuration limits for entity counts and sizes when these limits are explicitly set to zero, bypassing intended restrictions. This oversight allows for unbounded entity expansion, consuming excessive memory and leading to a Denial of Service (DoS) condition, which makes the application unavailable to legitimate users.
Remediation
For more about Red Hat Developer Hub, see References links
Optional official sources
National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.
Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.
Official European source
ENISA European Vulnerability Database
Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.
1 current
ENISA EUVD identifier
EUVD-2026-20080
No EUVD known-exploited evidence
ENISA has published the identifier mapping but no EUVD description has been stored yet.
EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix
Medium technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 4 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Fix availability varies by product
01
What, why and how
fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. From version 4.0.0-beta.3 to before version 5.5.7, the DocTypeReader in fast-xml-parser uses JavaScript truthy checks to evaluate maxEntityCount and maxEntitySize configuration limits. When a developer explicitly sets either limit to 0 — intending to disallow all entities or restrict entity size to zero bytes — the falsy nature of 0 in JavaScript causes the guard conditions to short-circuit, completely bypassing the limits. An attacker who can supply XML input to such an application can trigger unbounded entity expansion, leading to memory exhaustion and denial of service. This issue has been patched in version 5.5.7.
What
fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. From version 4.0.0-beta.3 to before version 5.5.7, the DocTypeReader in fast-xml-parser uses JavaScript truthy checks to evaluate maxEntityCount and maxEntitySize configuration limits. When a developer explicitly sets either limit to 0 — intending to disallow all entities or restrict entity size to zero bytes — the falsy nature of 0 in JavaScript causes the guard conditions to short-circuit, completely bypassing the limits. An attacker who can supply XML input to such an application can trigger unbounded entity expansion, leading to memory exhaustion and denial of service. This issue has been patched in version 5.5.7.
Why
The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
What
fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. From version 4.0.0-beta.3 to before version 5.5.7, the DocTypeReader in fast-xml-parser uses JavaScript truthy checks to evaluate maxEntityCount and maxEntitySize configuration limits. When a developer explicitly sets either limit to 0 — intending to disallow all entities or restrict entity size to zero bytes — the falsy nature of 0 in JavaScript causes the guard conditions to short-circuit, completely bypassing the limits. An attacker who can supply XML input to such an application can trigger unbounded entity expansion, leading to memory exhaustion and denial of service. This issue has been patched in version 5.5.7.
Why
The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No confirmed evidence
No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.Reference recorded
A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.
Likely attack path
a network path → Improper Validation of Specified Quantity in Input → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness ?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-1284: Improper Validation of Specified Quantity in Input. The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.
CVSS vector ?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-1284Public exploit reference
A
Official authority intelligence
Only matched European and national findings are included. Language selectors and unavailable sources are omitted.
ENISA EUVD · EUVD-2026-20080Official EUVD mapping
0 linked advisory records.
Official EUVD record ↗BSI · German · WID-SEC-2026-1407IBM App Connect Enterprise Certified Container: Mehrere Schwachstellen
Ein Angreifer kann mehrere Schwachstellen in IBM App Connect Enterprise Certified Container ausnutzen, um beliebigen Code auszuführen, Sicherheitsmaßnahmen zu umgehen, Cross-Site-Scripting-Angriffe durchzuführen, Daten zu manipulieren, vertrauliche Informationen offenzulegen oder einen Denial-of-Service-Zustand zu verursachen.
Official advisory ↗Cyber Security Agency of Singapore · English · CSA-SB-20260325Security Bulletin 25 Mar 2026
The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 25 Mar 2026, published on 25 March 2026. Open the linked bulletin for the product, severity and reference information published in that issue.
Official advisory ↗CERT-FR · French · CERTFR-2026-AVI-0667Multiples vulnérabilités dans les produits IBM
Operational remediation based on structured source evidence.
Status ?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
A mitigation or workaround reference is available from the source linked below; validate it against the affected product and version.
04
Evidence and provenance
Published 24 Mar 2026 · Last source change 25 Mar 2026, 14:28 UTC · CWE-1284 · Improper Validation of Specified Quantity in Input
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source ?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-20080
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD enriched
Core structured fields are present and their contributing authorities are shown above.
Affected versionsThe structured affected or fixed version information changed.
Before
>= 4.0.0-beta.3, < 5.5.7 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
After
>= 4.0.0-beta.3, < 5.5.7 · Fixed: For more about Red Hat Developer Hub, see References links
Affected versionsThe structured affected or fixed version information changed.
Before
mta/mta-ui-rhel9 as a component of Migration Toolkit for Applications 8; advanced-cluster-security/rhacs-main-rhel8 as a component of Red Hat Advanced Cluster Security 4; apicurio/apicurio-registry-ui-rhel8 as a component of Red Hat Data Grid 8; apicurio/apicurio-registry-ui-rhel9 as a component of Red Hat Data Grid 8; rhdh/backstage-community-plugin-catalog-backend-module-scaffolder-relation-processor as a component of Red Hat Developer Hub; rhoai/odh-mlflow-rhel9 as a component of Red Hat OpenShift AI (RHOAI); odf4/mcg-core-rhel9 as a component of Red Hat Openshift Data Foundation 4; odf4/ocs-client-console-rhel9 as a component of Red Hat Openshift Data Foundation 4; odf4/odf-console-rhel9 as a component of Red Hat Openshift Data Foundation 4; odf4/odf-multicluster-console-rhel9 as a component of Red Hat Openshift Data Foundation 4; openshift-gitops-1/argocd-rhel8 as a component of Red Hat OpenShift GitOps; openshift-gitops-1/argocd-rhel9 as a component of Red Hat OpenShift GitOps; container-native-virtualization/kubevirt-console-plugin as a component of Red Hat OpenShift Virtualization 4; container-native-virtualization/kubevirt-console-plugin-rhel9 as a component of Red Hat OpenShift Virtualization 4; satellite/iop-host-inventory-frontend-rhel9 as a component of Red Hat Satellite 6; satellite/iop-vulnerability-frontend-rhel9 as a component of Red Hat Satellite 6; ansible-automation-platform/automation-portal as a component of Self-service automation portal 2 · Fixed: registry.redhat.io/rhdh/rhdh-hub-rhel9@sha256:b99622b2ec913bdf7ad25a7a9919fbf07a6a177548b3f486acf648c533ca4f22_amd64 as a component of Red Hat Developer Hub 1.10
After
mta/mta-ui-rhel9 as a component of Migration Toolkit for Applications 8; advanced-cluster-security/rhacs-main-rhel8 as a component of Red Hat Advanced Cluster Security 4; apicurio/apicurio-registry-ui-rhel8 as a component of Red Hat Data Grid 8; apicurio/apicurio-registry-ui-rhel9 as a component of Red Hat Data Grid 8; rhdh/backstage-community-plugin-catalog-backend-module-scaffolder-relation-processor as a component of Red Hat Developer Hub; rhoai/odh-mlflow-rhel9 as a component of Red Hat OpenShift AI (RHOAI); openshift-gitops-1/argocd-rhel8 as a component of Red Hat OpenShift GitOps; openshift-gitops-1/argocd-rhel9 as a component of Red Hat OpenShift GitOps; container-native-virtualization/kubevirt-console-plugin as a component of Red Hat OpenShift Virtualization 4; container-native-virtualization/kubevirt-console-plugin-rhel9 as a component of Red Hat OpenShift Virtualization 4; satellite/iop-host-inventory-frontend-rhel9 as a component of Red Hat Satellite 6; satellite/iop-vulnerability-frontend-rhel9 as a component of Red Hat Satellite 6; ansible-automation-platform/automation-portal as a component of Self-service automation portal 2 · Fixed: registry.redhat.io/rhdh/rhdh-hub-rhel9@sha256:b99622b2ec913bdf7ad25a7a9919fbf07a6a177548b3f486acf648c533ca4f22_amd64 as a component of Red Hat Developer Hub 1.10; registry.redhat.io/odf4/cephcsi-rhel9-operator@sha256:21b851833c425cd0638fa0d97672b30481fe6196a38817955500f10f3516acaa_arm64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/cephcsi-rhel9-operator@sha256:4e29a09b15c2149d96e02b302dfa5c89d88e647467427f251d7dcc949710a153_s390x as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/cephcsi-rhel9-operator@sha256:7bbc972cffbd7c92a685e1cfb73365b261908046ccd7b712659b9b47737dfafa_ppc64le as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/cephcsi-rhel9-operator@sha256:dd66f2aabe08104f33b6ed32786947f9b91c37404d06b46838397c8c791dad0a_amd64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/cephcsi-rhel9@sha256:5e63bdd0b4345a25ed76efcc62a068f88b0c688328713e1711ca4cac73f96d76_s390x as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/cephcsi-rhel9@sha256:5eeddca3c800ec55d4d7dd479cfcd1751394b40e481b86433cd3838d2170952c_ppc64le as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/cephcsi-rhel9@sha256:fd06b75eb32cf69d0ab0c18eb922d540f0362d12aec3a9029fa77e13f307cb3f_amd64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/mcg-core-rhel9@sha256:2156c85468c3bd37a4a9cec2538aaf529fc4317b1cd56705c4f39247dbc1d1ff_ppc64le as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/mcg-core-rhel9@sha256:3701ca9bcf39e032702226a25a2d1a1ceedb2c9dc9e5bcfedc0104ad9d11e8c2_amd64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/mcg-core-rhel9@sha256:86da6a6280816bc50f36041e7a979274c3a5b27a63bccf15507e1f66afb49464_s390x as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/mcg-rhel9-operator@sha256:0b4d42e8e476f817548053fc8363084c60e7c4c8278fdad46f89752c422318f7_amd64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/mcg-rhel9-operator@sha256:0bdec5fd8a2a4df637a6dbe6da3c7aa7dd98e424f6ccac1b666069240c3c6a2b_s390x as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/mcg-rhel9-operator@sha256:55d1e96c46d7e18200d64878901161cad4a2e5ddb1bd2ab35e21d0e63743db4a_ppc64le as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/mcg-rhel9-operator@sha256:65e384de217a7ac0752bd0bd7e39f2a16d3d55023b7e389dbfd6223e3050caef_arm64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-client-console-rhel9@sha256:13e09d8d7196c9c24af4756aecc76226f5193a6fb8efd6314d72afb1ee8b08af_ppc64le as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-client-console-rhel9@sha256:339175c0cf3bfc97a1b5f1fd40be12b124b9eadd7e3990b40c01cc2c8f202088_amd64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-client-console-rhel9@sha256:bb3516bbf6e6eeb5a9949de05c19d80a903533c0fcf4a756ff7f68af793a516c_s390x as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-client-rhel9-operator@sha256:06e77572fb0925499e831cea92e04009dba079413374794f89087484bce54ac9_amd64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-client-rhel9-operator@sha256:8251a421792fffa707904b2d23b15b11fe0e2d85b526824e7c64d74c90a582d0_arm64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-client-rhel9-operator@sha256:bec7bd0e64563d9df240e1be1b717db34ad76abbe1665404cb77f26d6b1cdc36_ppc64le as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-client-rhel9-operator@sha256:caf3ccf3985ba2b9308567885b17eb0ab34ffbbacc194b6459fc0f9f8a612974_s390x as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-metrics-exporter-rhel9@sha256:126f56171f915a0a53f6f5dcb315855911aa40a91c76a5f8188b7a7a103350d5_s390x as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-metrics-exporter-rhel9@sha256:3457ba8cafdf27bfd21fdf20314da9141b263034026052d5543846397b38eafd_amd64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-metrics-exporter-rhel9@sha256:d31a9f14f99c50f2a79774147289e5715e321f2db4c9b4ef938feaad31882c7c_ppc64le as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-rhel9-operator@sha256:02b74a58540b0a6cb4e887843fa2b6adad58506af305b73f78b415ed5eb26cf5_ppc64le as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-rhel9-operator@sha256:3371d5a58aad8a88b93c9d4ba0bd207ef1b995198fdc5b14d458ce9945556299_arm64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-rhel9-operator@sha256:453592b92ed196134663051a8dd4c0141eb21811753298ab8b103ff68bee139c_s390x as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/ocs-rhel9-operator@sha256:6f7fd5670c320a901a22ceed54af4108a297179da36cac6b56150df491ab9381_amd64 as a component of Red Hat Openshift Data Foundation 4.18; registry.redhat.io/odf4/odf-cli-rhel9@sha256:298eec5fa31c1f77a8e6e69fbeda1e6aff39a54d93db279e85117f00970649c3_amd64 as a component of Red Hat Openshift Data Foundation 4.18; and 39 more
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.