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Overview

fast-xml-parser is a Validate XML, Parse XML, Build XML without C/C++ based libraries

Affected versions of this package are vulnerable to XML Entity Expansion in replaceEntitiesValue() when handling excessive DOCTYPE input. An attacker can cause excessive resource consumption and make the application unresponsive by submitting malicious XML input with large text entities referenced multiple times. This is a bypass for Billion Laughs protection in DocTypeReader.js, which prevents excessive referencing within and entity, but doesn't prevent repeated expansion of large entities.

Workaround

This vulnerability can be mitigated by disabling DOCTYPE parsing using the processEntities: false option.

PoC

const { XMLParser } = require('fast-xml-parser');

const entity = 'A'.repeat(1000);
const refs = '&big;'.repeat(100);
const xml = `<!DOCTYPE foo [<!ENTITY big "${entity}">]><root>${refs}</root>`;

console.time('parse');
new XMLParser().parse(xml);
console.timeEnd('parse');

Details

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

• High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

• Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package

Remediation

Upgrade fast-xml-parser to version 4.5.4, 5.3.6 or higher.

References

• GitHub Commit
• GitHub Release

Overview

fast-xml-parser is a Validate XML, Parse XML, Build XML without C/C++ based libraries

Affected versions of this package are vulnerable to XML Entity Expansion in the replaceEntitiesValue() function, which doesn't protect unlimited expansion of numeric entities the way it does DOCTYPE data (as described and fixed for CVE-2026-26278). An attacker can exhaust system memory and CPU resources by submitting XML input containing a large number of numeric character references - &#NNN; and &#xHH;.

Note: This is a bypass for the fix to the DOCTYPE expansion vulnerability in 5.3.6.

Details

Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

• High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

• Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package

Remediation

Upgrade fast-xml-parser to version 5.5.6 or higher.

References

• GitHub Commit
• GitHub Release

Overview

music-metadata is a Music metadata parser for Node.js, supporting virtual any audio and tag format.

Affected versions of this package are vulnerable to Infinite loop through the parseExtensionObject process in the ASF parser when handling a sub-object with objectSize = 0. An attacker can cause the application to hang indefinitely by providing a specially crafted .asf file that triggers an infinite loop during parsing.

Remediation

Upgrade music-metadata to version 11.12.3 or higher.

References

• GitHub Commit
• GitHub PR
• GitHub Release

Overview

qs is a querystring parser that supports nesting and arrays, with a depth limit.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling via improper enforcement of the arrayLimit option in bracket notation parsing. An attacker can exhaust server memory and cause application unavailability by submitting a large number of bracket notation parameters - like a[]=1&a[]=2 - in a single HTTP request.

PoC

const qs = require('qs');
const attack = 'a[]=' + Array(10000).fill('x').join('&a[]=');
const result = qs.parse(attack, { arrayLimit: 100 });
console.log(result.a.length);  // Output: 10000 (should be max 100)

Remediation

Upgrade qs to version 6.14.1 or higher.

References

• GitHub Commit

Overview

undici is an An HTTP/1.1 client, written from scratch for Node.js

Affected versions of this package are vulnerable to Improper Handling of Highly Compressed Data (Data Amplification) in the PerMessageDeflate.decompress() method of the permessage-deflate extension. An attacker can cause excessive memory usage by sending specially crafted compressed WebSocket frames that decompress to a very large size, potentially leading to process crashes or unresponsiveness.

Remediation

Upgrade undici to version 6.24.0, 7.24.0 or higher.

References

• GitHub Commit
• HackerOne Report

Overview

undici is an An HTTP/1.1 client, written from scratch for Node.js

Affected versions of this package are vulnerable to Uncaught Exception through improper validation of the server_max_window_bits parameter in the permessage-deflate extension. An attacker can cause the process to terminate unexpectedly by sending a maliciously crafted value outside the valid range, which triggers an unhandled exception when the client attempts to create a zlib InflateRaw instance.

Remediation

Upgrade undici to version 6.24.0, 7.24.0 or higher.

References

• GitHub Commit
• HackerOne Report

Overview

fast-xml-parser is a Validate XML, Parse XML, Build XML without C/C++ based libraries

Affected versions of this package are vulnerable to Improper Validation of Specified Quantity in Input in the DocTypeReader component when the maxEntityCount or maxEntitySize configuration options are explicitly set to 0. Due to JavaScript's falsy evaluation, the intended limits are bypassed. An attacker can cause unbounded entity expansion and exhaust server memory by supplying crafted XML input containing numerous large entities.

Note:

This is only exploitable if the application is configured with processEntities enabled and either maxEntityCount or maxEntitySize set to 0.

PoC

const { XMLParser } = require("fast-xml-parser");

// Developer intends: "no entities allowed at all"
const parser = new XMLParser({
  processEntities: {
    enabled: true,
    maxEntityCount: 0,    // should mean "zero entities allowed"
    maxEntitySize: 0       // should mean "zero-length entities only"
  }
});

// Generate XML with many large entities
let entities = "";
for (let i = 0; i < 1000; i++) {
  entities += `<!ENTITY e${i} "${"A".repeat(100000)}">`;
}

const xml = `<?xml version="1.0"?>
<!DOCTYPE foo [
  ${entities}
]>
<foo>&e0;</foo>`;

// This should throw "Entity count exceeds maximum" but does not
try {
  const result = parser.parse(xml);
  console.log("VULNERABLE: parsed without error, entities bypassed limits");
} catch (e) {
  console.log("SAFE:", e.message);
}

// Control test: setting maxEntityCount to 1 correctly blocks
const safeParser = new XMLParser({
  processEntities: {
    enabled: true,
    maxEntityCount: 1,
    maxEntitySize: 100
  }
});

try {
  safeParser.parse(xml);
  console.log("ERROR: should have thrown");
} catch (e) {
  console.log("CONTROL:", e.message);  // "Entity count (2) exceeds maximum allowed (1)"
}

Remediation

Upgrade fast-xml-parser to version 5.5.7 or higher.

References

• GitHub Advisory
• GitHub Commit

Overview

qs is a querystring parser that supports nesting and arrays, with a depth limit.

Affected versions of this package are vulnerable to Allocation of Resources Without Limits or Throttling via the parseArrayValue function when the comma option is in use. An attacker can exhaust system memory by submitting a parameter containing a large number of comma-separated values, resulting in the allocation of excessively large arrays.

Note: This is only exploitable if the comma option is explicitly set to true. arrayLimit is properly enforced for index and bracket notation.

PoC

const qs = require('qs');

const payload = 'a=' + ','.repeat(25);  // 26 elements after split (bypasses arrayLimit: 5)
const options = { comma: true, arrayLimit: 5, throwOnLimitExceeded: true };

try {
  const result = qs.parse(payload, options);
  console.log(result.a.length);  // Outputs: 26 (bypass successful)
} catch (e) {
  console.log('Limit enforced:', e.message);  // Not thrown
}

Remediation

Upgrade qs to version 6.14.2 or higher.

References

• GitHub Commit

Overview

uuid is a RFC4122 (v1, v4, and v5) compliant UUID library.

Affected versions of this package are vulnerable to Improper Validation of Specified Index, Position, or Offset in Input due to accepting external output buffers but not rejecting out-of-range writes (small buf or large offset). This inconsistency allows silent partial writes into caller-provided buffers.

PoC

cd /home/StrawHat/uuid
npm ci
npm run build

node --input-type=module -e "
import {v4,v5,v6} from './dist-node/index.js';
const ns='6ba7b810-9dad-11d1-80b4-00c04fd430c8';
for (const [name,fn] of [
  ['v4',()=>v4({},new Uint8Array(8),4)],
  ['v5',()=>v5('x',ns,new Uint8Array(8),4)],
  ['v6',()=>v6({},new Uint8Array(8),4)],
]) {
  try { fn(); console.log(name,'NO_THROW'); }
  catch(e){ console.log(name,'THREW',e.name); }
}"

Remediation

Upgrade uuid to version 11.1.1, 14.0.0 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Release

Overview

fast-xml-parser is a Validate XML, Parse XML, Build XML without C/C++ based libraries

Affected versions of this package are vulnerable to Incorrect Regular Expression in the entity parsing RegEx in DOCTYPE declarations. An attacker can inject arbitrary values that override built-in XML entities by crafting entity names containing ., which is interpreted as a regex wildcard, allowing malicious content to be substituted in place of standard entities when the XML is parsed and subsequently rendered or used in sensitive contexts.

Remediation

Upgrade fast-xml-parser to version 4.5.4, 5.3.5 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Release