CVE-2026-26278
February 19, 2026
fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. In versions 4.1.3 through 5.3.5, the XML parser can be forced to do an unlimited amount of entity expansion. With a very small XML input, it’s possible to make the parser spend seconds or even minutes processing a single request, effectively freezing the application. Version 5.3.6 fixes the issue. As a workaround, avoid using DOCTYPE parsing by "processEntities: false" option.
Affected Packages
https://github.com/NaturalIntelligence/fast-xml-parser.git (GITHUB):
Affected version(s) >=v4.1.3 <v5.3.6Fix Suggestion:
Update to version v5.3.6fast-xml-parser (NPM):
Affected version(s) >=4.1.3 <4.5.4Fix Suggestion:
Update to version 4.5.4fast-xml-parser (NPM):
Affected version(s) >=5.0.0 <5.3.6Fix Suggestion:
Update to version 5.3.6Related Resources (5)
Do you need more information?
Contact UsCVSS v4
Base Score:
8.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Weakness Type (CWE)
Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
EPSS
Base Score:
0.06
