GHSA-6w63-h3fj-q4vw CVE-2023-34104
fast-xml-parser vulnerable to Regex Injection via Doctype Entities
- Severity
- 7.5 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 1.13%
- Chance of exploitation in the next 30 days. Higher than 66.31% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
4.2.4- Upgrade fast-xml-parser to this version or later
Description
Impact
"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 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.
Patches
The problem has been resolved in v4.2.4
Workarounds
Avoid using DOCTYPE parsing by processEntities: false option.
Affected versions
npm
| Package | Vulnerable | Fixed in |
|---|---|---|
| fast-xml-parser | >= 4.1.3, < 4.2.4 |
4.2.4 |
| fast-xml-parser | >= 4.1.3, < 4.2.4 |
4.2.4 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
fast-xml-parser npm → 4.2.4
- npm
npm install fast-xml-parser@4.2.4- yarn
yarn add fast-xml-parser@4.2.4- pnpm
pnpm add fast-xml-parser@4.2.4
Severity breakdown
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Weakness
CWE-400: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How to prevent it
- Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
- Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
- Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
- Implementation: Ensure that all failures in resource allocation place the system into a safe posture.
CWE-1333: Inefficient Regular Expression Complexity
The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
How to prevent it
- Architecture and Design: Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
- System Configuration: Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
- Implementation: Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
- Implementation: Limit the length of the input that the regular expression will process.
References
Advisories
Fixes and patches
Packages
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-8r6m-32jq-jx6q fast-xml-parser: Repeated DOCTYPE declarations reset entity expansion limits | High | Also affects fast-xml-parser |
| GHSA-gh4j-gqv2-49f6 fast-xml-parser XMLBuilder: XML Comment and CDATA Injection via Unescaped Delimiters | Medium | Also affects fast-xml-parser |
| GHSA-jp2q-39xq-3w4g Entity Expansion Limits Bypassed When Set to Zero Due to JavaScript Falsy Evaluation in fast-xml-parser | Medium | Also affects fast-xml-parser |
| GHSA-8gc5-j5rx-235r fast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278) | High | Also affects fast-xml-parser |
| GHSA-fj3w-jwp8-x2g3 fast-xml-parser has stack overflow in XMLBuilder with preserveOrder | Low | Also affects fast-xml-parser |
| GHSA-m7jm-9gc2-mpf2 fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names | Critical | Also affects fast-xml-parser |
| GHSA-jmr7-xgp7-cmfj fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit) | High | Also affects fast-xml-parser |
| GHSA-37qj-frw5-hhjh fast-xml-parser has RangeError DoS Numeric Entities Bug | High | Also affects fast-xml-parser |
Credits: 7085, levpachmanov
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