NaturalIntelligence fast-xml-parser up to 5.5.6 improper validation of specified quantity in input

CVSS Meta Temp Score
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CTI Interest Score
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4.7$0-$5k1.55

Summaryinfo

A vulnerability categorized as problematic has been discovered in NaturalIntelligence fast-xml-parser up to 5.5.6. The affected element is an unknown function. Executing a manipulation can lead to improper validation of specified quantity in input. The identification of this vulnerability is CVE-2026-33349. The attack may be launched remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in NaturalIntelligence fast-xml-parser up to 5.5.6. This vulnerability affects an unknown functionality. The manipulation with an unknown input leads to a improper validation of specified quantity in input vulnerability. The CWE definition for the vulnerability is CWE-1284. 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. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-33349 since 03/18/2026. The exploitation appears to be difficult. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available.

The vulnerability scanner Nessus provides a plugin with the ID 304213 (Linux Distros Unpatched Vulnerability : CVE-2026-33349), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.5.7 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (304213). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

Name

Version

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 4.8
VulDB Meta Temp Score: 4.7

VulDB Base Score: 3.7
VulDB Temp Score: 3.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 5.9
CNA Vector (GitHub_M): 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Improper validation of specified quantity in input
CWE: CWE-1284 / CWE-703
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 304213
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2026-33349

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: fast-xml-parser 5.5.7

Timelineinfo

03/18/2026 CVE reserved
03/24/2026 +6 days Advisory disclosed
03/24/2026 +0 days VulDB entry created
03/29/2026 +5 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-33349 (🔒)
GCVE (CVE): GCVE-0-2026-33349
GCVE (VulDB): GCVE-100-352864

Entryinfo

Created: 03/24/2026 20:59
Updated: 03/29/2026 11:47
Changes: 03/24/2026 20:59 (62), 03/29/2026 11:35 (1), 03/29/2026 11:47 (2)
Complete: 🔍
Cache ID: 216:19A:103

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