fast-xml-parser XML Entity Expansion DoS 4.1.3-5.3.5
CVE-2026-26278 Published on February 19, 2026
fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)
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, its 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.
Vulnerability Analysis
CVE-2026-26278 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is a XEE Vulnerability?
The software uses XML documents and allows their structure to be defined with a Document Type Definition (DTD), but it does not properly control the number of recursive definitions of entities. If the DTD contains a large number of nested or recursive entities, this can lead to explosive growth of data when parsed, causing a denial of service.
CVE-2026-26278 has been classified to as a XEE vulnerability or weakness.
Products Associated with CVE-2026-26278
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