CVE-2026-33036

HIGH EPSS 43.2%
Published Mar 20, 20263mo ago · Modified Mar 23, 20263mo ago
7.5 CVSS 3.1
High
Find Similar
Published Mar 20, 2026 3mo ago
Last Modified Mar 23, 2026 3mo ago

Description

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.

CVSS Details

Base Score
7.5
Exploitability
3.9
Impact
3.6
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality None
Integrity None
Availability High

Threat Intelligence

EPSS Exploit Probability
43.2% percentile
Exploit & Patch Status
Public Exploit Known
Patch Available

Weaknesses 1

CWE-776

Affected Products 8

VendorProductVersionRange
naturalintelligencefast-xml-parser*≥4.0.1  –  <5.5.6
naturalintelligencefast-xml-parser4.0.0any
naturalintelligencefast-xml-parser4.0.0any
naturalintelligencefast-xml-parser4.0.0any
naturalintelligencefast-xml-parser4.0.0any
naturalintelligencefast-xml-parser4.0.0any
naturalintelligencefast-xml-parser4.0.0any
naturalintelligencefast-xml-parser4.0.0any

References 3

  • github.com https://github.com/NaturalIntelligence/fast-xml-parser/commit/bd26122c838e6a55e7d7ac49b4ccc01a49999a01
    Patch
  • github.com https://github.com/NaturalIntelligence/fast-xml-parser/releases/tag/v5.5.6
    ProductRelease Notes
  • github.com https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-8gc5-j5rx-235r
    ExploitMitigationVendor Advisory

Remediation

  • github.com https://github.com/NaturalIntelligence/fast-xml-parser/commit/bd26122c838e6a55e7d7ac49b4ccc01a49999a01
    Patch