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NVD / CVE Program· CNA GitHub_M

CVE-2026-33036: fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278)

Noroxi assessment

Priority: Monitor (action score 30/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.59% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: NaturalIntelligence fast-xml-parser 5.5.6.

Low priority for now. Upgrade to NaturalIntelligence fast-xml-parser 5.5.6 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Versions 4.0.0-beta.3 through 5.5.5 contain a bypass vulnerability where numeric character references (&#NNN;, &#xHH;) and standard XML entities completely evade the entity expansion limits (e.g., maxTotalExpansions, maxExpandedLength) added to fix CVE-2026-26278, enabling XML entity expansion Denial of Service. The root cause is that replaceEntitiesValue() in OrderedObjParser.js only enforces expansion counting on DOCTYPE-defined entities while the lastEntities loop handling numeric/standard entities performs no counting at all. An attacker supplying 1M numeric entity references like A can force ~147MB of memory allocation and heavy CPU usage, potentially crashing the process—even when developers have configured strict limits. This issue has been fixed in version 5.5.6.

HighCVSS 7.5 · v3.1—No exploit Fix available
Published
Mar 20, 2026
Updated
Jun 17, 2026
EPSS
0.5% · 48th percentile

Report tools

JSON

Action score

30

Monitor

Low priority for now.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.5%

CISA SSVC decision

Exploitation
proof of concept
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
7.5
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-33036

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
naturalintelligencefast-xml-parser

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • naturalintelligence fast-xml-parser4.0.1 and later · before 5.5.6
  • naturalintelligence fast-xml-parser4.0.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • NaturalIntelligence fast-xml-parser

    • >= 4.0.0-beta.3, < 5.5.6affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12node-webfontfrom 0—
npmfast-xml-parserfrom 4.0.0-beta.3 · before 4.5.54.5.5
npmfast-xml-parserfrom 5.0.0 · before 5.5.65.5.6
openSUSE:Tumbleweedheroic-games-launcherbefore 2.20.1-4.12.20.1-4.1

Same product

naturalintelligence: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-25896fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names
    37Monitor
  • CVE-2026-73569fast-xml-parser: Repeated DOCTYPE declarations reset entity expansion limits
    34Monitor
  • CVE-2026-26278fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)
    30Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-25128Jan 30, 2026 · fast-xml-parser has RangeError DoS Numeric Entities Bug
    30Monitor
  • ← EarlierCVE-2026-27942Feb 25, 2026 · fast-xml-parser has stack overflow in XMLBuilder with preserveOrder
    10Monitor
  • Later →CVE-2026-33349Mar 24, 2026 · fast-xml-parser: Entity Expansion Limits Bypassed When Set to Zero Due to JavaScript Falsy Evaluation
    23Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
NaturalIntelligence fast-xml-parser5.5.6 · descriptionVendor (CNA)
npm:fast-xml-parser4.5.5Package registry (OSV)
npm:fast-xml-parser5.5.6Package registry (OSV)
opensuse:heroic-games-launcher2.20.1-4.1 · openSUSE:TumbleweedPackage registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-73569146 days apartfast-xml-parser: Repeated DOCTYPE declarations reset entity expansion limits
    34Monitor
  • CVE-2026-2627829 days apartfast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)
    30Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-776 · Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records