fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. From 5.9.3 until 5.10.1, src/xmlparser/OrderedObjParser.js processes multiple DOCTYPE declarations within a single XML document and passes each declaration's entities through addInputEntities(). addInputEntities() resets maxTotalExpansions and maxExpandedLength every time it is called, allowing additional DOCTYPE declarations to repeatedly reset the configured entity-expansion limits during one parse operation. A crafted XML document can then cause excessive CPU use, event-loop blocking, memory exhaustion, and process termination. This issue is fixed in version 5.10.1.

Affected: npm: fast-xml-parser

### Impact `fast-xml-parser` processes multiple "DOCTYPE" declarations within a single XML document. Each declaration passes its entities to `@nodable/entities` through `addInputEntities()`.

`addInputEntities()` resets the entity expansion counters every time it is called. An attacker can therefore insert additional DOCTYPE declarations to repeatedly reset maxTotalExpansions and maxExpandedLength during one parse operation.

This allows a crafted XML document to exceed the configured entity-expansion limits and can cause excessive CPU use, event-loop blocking, memory exhaustion, and process termination.

### Workarounds - Manually check if multiple DOCTYPEs are not present in input contents - Update to v5.10.1 - Keep `processEntity` flag off

fast-uri: Fast-uri: Security policy bypass due to URL parsing inconsistency github.com/open-telemetry/opentelemetry-go: go.opentelemetry.io/otel/baggage: go.opentelemetry.io/otel/propagation: OpenTelemetry-Go: Denial of Service via oversized baggage headers golang.org/x/text: golang.org/x/text: Denial of Service via invalid UTF-8 input fast-xml-parser: fast-xml-parser: Denial of Service via repeated DOCTYPE declarations

Affected: Ubuntu:24.04:LTS: node-webfont, Ubuntu:26.04:LTS: node-webfont

fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. From 5.9.3 until 5.10.1, src/xmlparser/OrderedObjParser.js processes multiple DOCTYPE declarations within a single XML document and passes each declaration's entities through addInputEntities(). addInputEntities() resets maxTotalExpansions and maxExpandedLength every time it is called, allowing additional DOCTYPE declarations to repeatedly reset the configured entity-expansion limits during one parse operation. A crafted XML document can then cause excessive CPU use, event-loop blocking, memory exhaustion, and process termination. This issue is fixed in version 5.10.1.

Ein entfernter, anonymer Angreifer kann eine Schwachstelle in IBM App Connect Enterprise ausnutzen, um einen Denial of Service Angriff durchzuführen.