CVE-2026-27942 fast-xml-parser has stack overflow in XMLBuilder with preserveOrder
An attacker can cause a stack overflow crash in fast-xml-parser by using the XML builder with preserveOrder enabled, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27942?
CVE-2026-27942 is a low-severity denial of service vulnerability in NaturalIntelligence fast-xml-parser, published on 26 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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. Prior to version 5.3.8, the application crashes with stack overflow when user use XML builder with `preserveOrder:true`. Version 5.3.8 fixes the issue. As a workaround, use XML builder with `preserveOrder:false` or check the input data before passing to builder.
Weakness: CWE-120
Which versions are affected by CVE-2026-27942?
4 open source packages ship an affected version, including fast-xml-parser. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
fast-xml-parser npm | From 4.0.0-beta.0 | 4.5.4 |
fast-xml-parser npm | From 4.0.0-beta.0 | 4.5.4 |
fast-xml-parser npm | From 5.0.0 | 5.3.8 |
fast-xml-parser npm | From 5.0.0 | 5.3.8 |
Products include Naturalintelligence Fast-Xml-Parser.
How do I fix CVE-2026-27942?
Upgrade fast-xml-parser to a fixed version for your release line: 4.5.4 or 5.3.8.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-27942 being exploited?
There is no known exploitation of CVE-2026-27942 in the wild and no public exploit code.
Other vulnerabilities in NaturalIntelligence fast-xml-parser
- CVE-2026-25896 fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names
- CVE-2026-33036 fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278)
- CVE-2026-26278 fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)
- CVE-2026-25128 fast-xml-parser has RangeError DoS Numeric Entities Bug
- CVE-2024-41818 ReDOS at currency parsing fast-xml-parser
Sources
Also known as CLEANSTART-2026-DD01525, CLEANSTART-2026-ZT14752, CLSA-2026-1789289706, DEBIAN-CVE-2026-27942, ECHO-a140-4efb-7c2a, GHSA-fj3w-jwp8-x2g3 and 17 more.