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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 Uncaught Exception in the numeric entity processing when parsing XML containing out-of-range entity code points. An attacker can cause the application to crash by submitting specially crafted XML input that triggers an uncaught exception.

Remediation

Upgrade fast-xml-parser to version 5.3.4 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 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 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 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 5.3.5 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Release