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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., &#​9999999; or �). This causes the parser to throw an uncaught exception, crashing any application that processes untrusted XML input.
Details
The vulnerability exists in /src/xmlparser/OrderedObjParser.js at lines 44-45:
The String.fromCodePoint() method throws a RangeError when the code point exceeds the valid Unicode range (0 to 0x10FFFF / 1114111). The regex patterns can capture values far exceeding this:
[0-9]{1,7} matches up to 9,999,999
[0-9a-fA-F]{1,6} matches up to 0xFFFFFF (16,777,215)
The entity replacement in replaceEntitiesValue() (line 452) has no try-catch:
val=val.replace(entity.regex,entity.val);
This causes the RangeError to propagate uncaught, crashing the parser and any application using it.
consthttp=require('http');const{ XMLParser }=require('fast-xml-parser');constparser=newXMLParser({processEntities: true,htmlEntities: true});http.createServer((req,res)=>{if(req.method==='POST'&&req.url==='/parse'){letbody='';req.on('data',c=>body+=c);req.on('end',()=>{constresult=parser.parse(body);// No try-catch - will crash!res.end(JSON.stringify(result));});}else{res.end('POST /parse with XML body');}}).listen(3000,()=>console.log('http://localhost:3000'));
Run
# Setup
npm install
# Terminal 1: Start server
node server.js
# Terminal 2: Send malicious payload (server will crash)
curl -X POST -H "Content-Type: application/xml" -d '<?xml version="1.0"?><root>&#​9999999;</root>' http://localhost:3000/parse
Denial of Service (DoS):* Any application using fast-xml-parser to process untrusted XML input will crash when encountering malformed numeric entities. This affects:
API servers accepting XML payloads
File processors parsing uploaded XML files
Message queues consuming XML messages
RSS/Atom feed parsers
SOAP/XML-RPC services
A single malicious request is sufficient to crash the entire Node.js process, causing service disruption until manual restart.
renovatebot
changed the title
chore(deps): update dependency fast-xml-parser to v5.3.4 [security]
chore(deps): update dependency fast-xml-parser to v5.3.4 [security] - autoclosed
Jan 31, 2026
renovatebot
changed the title
chore(deps): update dependency fast-xml-parser to v5.3.4 [security] - autoclosed
chore(deps): update dependency fast-xml-parser to v5.3.4 [security]
Feb 6, 2026
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This PR contains the following updates:
5.2.5→5.3.4GitHub Vulnerability Alerts
CVE-2026-25128
Summary
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.,
&#​9999999;or�). This causes the parser to throw an uncaught exception, crashing any application that processes untrusted XML input.Details
The vulnerability exists in
/src/xmlparser/OrderedObjParser.jsat lines 44-45:The
String.fromCodePoint()method throws aRangeErrorwhen the code point exceeds the valid Unicode range (0 to 0x10FFFF / 1114111). The regex patterns can capture values far exceeding this:[0-9]{1,7}matches up to 9,999,999[0-9a-fA-F]{1,6}matches up to 0xFFFFFF (16,777,215)The entity replacement in
replaceEntitiesValue()(line 452) has no try-catch:This causes the RangeError to propagate uncaught, crashing the parser and any application using it.
PoC
Setup
Create a directory with these files:
package.json
{ "dependencies": { "fast-xml-parser": "^5.3.3" } }server.js
Run
Result
Server crashes with:
Alternative Payloads
Impact
Denial of Service (DoS):* Any application using fast-xml-parser to process untrusted XML input will crash when encountering malformed numeric entities. This affects:
A single malicious request is sufficient to crash the entire Node.js process, causing service disruption until manual restart.
Release Notes
NaturalIntelligence/fast-xml-parser (fast-xml-parser)
v5.3.4: fix: handle HTML numeric and hex entities when out of rangeCompare Source
v5.3.3: bug fix and performance improvementsCompare Source
v5.3.2Compare Source
v5.3.1Compare Source
v5.3.0Compare Source
Configuration
📅 Schedule: Branch creation - "" in timezone America/Vancouver, Automerge - At any time (no schedule defined).
🚦 Automerge: Enabled.
♻ Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.
🔕 Ignore: Close this PR and you won't be reminded about this update again.
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