CVE-2026-25128 fast-xml-parser has RangeError DoS Numeric Entities Bug
An attacker can crash applications using fast-xml-parser by sending XML with out-of-range numeric entities, causing an uncaught RangeError exception.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-25128?
CVE-2026-25128 is a high-severity denial of service vulnerability in NaturalIntelligence fast-xml-parser, published on 30 Jan 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. In versions 5.0.9 through 5.3.3, a RangeError vulnerability exists in the numeric entity processing of fast-xml-parser when parsing XML with out-of-range entity code points (e.g., `�` or `�`). This causes the parser to throw an uncaught exception, crashing any application that processes untrusted XML input. Version 5.3.4 fixes the issue.
Which versions are affected by CVE-2026-25128?
2 open source packages ship an affected version, including fast-xml-parser. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
fast-xml-parser npm | From 5.0.9 | 5.3.4 |
fast-xml-parser npm | From 5.0.9 | 5.3.4 |
Products include Naturalintelligence Fast-Xml-Parser.
How do I fix CVE-2026-25128?
Upgrade fast-xml-parser to 5.3.4 or later.
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-2026-25128 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25128 exists.
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-2024-41818 ReDOS at currency parsing fast-xml-parser
- CVE-2023-34104 Regex Injection via Doctype Entities
Sources
Also known as CLEANSTART-2026-HA50090, CLEANSTART-2026-XI72782, CLSA-2026-1774398086, CLSA-2026-1784856386, GHSA-37qj-frw5-hhjh, MINI-3q7m-3687-m58w and 12 more.