fast-xml-parser regex vulnerability patch could be improved from a safety perspective

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

not scored

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary This is a comment on https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-6w63-h3fj-q4vw and the patches fixing it. Details The code which validates a name calls the validator: https://github.com/NaturalIntelligence/fast-xml-parser/blob/ecf6016f9b48aec1a921e673158be0773d07283e/src/xmlparser/DocTypeReader.js#L145-L153 This checks for the presence of an invalid character. Such an approach is always risky, as it is so easy to forget to include an invalid character in the list. A safer approach is to validate entity names against the XML specification: https://www.w3.org/TR/xml11/#sec-common-syn - an ENTITY name is a Name: so the safest way to validate an entity name is to build a regex to represent this expression and check whether the name given matches the regex. (Something along the lines of /^[name start char class][name char class]$/.) There's probably a nice way to simplify the explicit list rather than typing it out verbatim using Unicode…

Published by the source

15 Jun 2023, 19:05 UTC

Last modified by the source

29 Nov 2023, 00:28 UTC

Source last checked

26 Oct 2026, 12:29 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-gpv5-7x3g-ghjv

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-gpv5-7x3g-ghjv

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# Patch Next advisory brief: GHSA-gpv5-7x3g-ghjv

Advisory: fast-xml-parser regex vulnerability patch could be improved from a safety perspective
IDs: GHSA-gpv5-7x3g-ghjv
Record: https://patchnext.com/advisories/ghsa-gpv5-7x3g-ghjv (revision 2, source checked 26 Oct 2026, 12:29 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: fast-xml-parser 4.2.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm fast-xml-parser: affected >= 4.2.4, <= 4.2.4; fixed in 4.2.5

## Suggested inspection (read-only)
- `npm ls fast-xml-parser --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on fast-xml-parser.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-gpv5-7x3g-ghjv (OSV record GHSA-gpv5-7x3g-ghjv lists affected ranges: npm fast-xml-parser >=4.2.4 <4.2.5 (fixed))
- Verified: https://github.com/advisories/GHSA-gpv5-7x3g-ghjv (GitHub-reviewed advisory GHSA-gpv5-7x3g-ghjv lists affected ranges: npm fast-xml-parser >=4.2.4 <=4.2.4)

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