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stack overflow in XMLBuilder with preserveOrder

Low
amitguptagwl published GHSA-fj3w-jwp8-x2g3 Feb 25, 2026

Package

npm fast-xml-parser (npm)

Affected versions

>=4.0.0-beta.0, <= 5.3.6

Patched versions

4.5.4, 5.3.7

Description

Impact

Application crashes with stack overflow when user use XML builder with prserveOrder:true for following or similar input

[{
    'foo': [
        { 'bar': [{ '@_V': 'baz' }] }
    ]
}]

Cause: arrToStr was not validating if the input is an array or a string and treating all non-array values as text content.
What kind of vulnerability is it? Who is impacted?

Patches

Yes in 5.3.8

Workarounds

Use XML builder with preserveOrder:false or check the input data before passing to builder.

References

Are there any links users can visit to find out more?

Severity

Low

CVE ID

CVE-2026-27942

Weaknesses

No CWEs