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Medium, CVSS 6.1amended

fast-xml-parser XMLBuilder: XML Comment and CDATA Injection via Unescaped Delimiters

CVE-2026-41650GHSA-gh4j-gqv2-49f6

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (fast-xml-parser 5.7.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS
  • CVE-2026-41650: 0.24% estimated exploitation activity in the next 30 days; percentile 14.96 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

fast-xml-parser XMLBuilder: Comment and CDATA Injection via Unescaped Delimiters Summary fast-xml-parser XMLBuilder does not escape the -- sequence in comment content or the ]] sequence in CDATA sections when building XML from JavaScript objects. This allows XML injection when user-controlled data flows into comments or CDATA elements, leading to XSS, SOAP injection, or data manipulation. Existing CVEs for fast-xml-parser cover different issues: - CVE-2023-26920: Prototype pollution (parser) - CVE-2023-34104: ReDoS (parser) - CVE-2026-27942: Stack overflow in XMLBuilder with preserveOrder - CVE-2026-25896: Entity encoding bypass via regex in DOCTYPE entities This finding covers unescaped comment/CDATA delimiters in XMLBuilder - a distinct vulnerability. Vulnerable Code File: src/fxb.js Compare with attribute/text escaping which IS properly handled via replaceEntitiesValue(). Proof of Concept Test 1: Comment Injection (XSS in SVG/HTML context) Output: Test 2: CDATA Injection (RSS…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-gh4j-gqv2-49f6

  2. Revision 1 · created ·

    Published from osv record GHSA-gh4j-gqv2-49f6

Agent brief

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# Patch Next advisory brief: CVE-2026-41650

Advisory: fast-xml-parser XMLBuilder: XML Comment and CDATA Injection via Unescaped Delimiters
IDs: CVE-2026-41650, GHSA-gh4j-gqv2-49f6
Record: https://patchnext.com/advisories/cve-2026-41650 (revision 2, source checked 26 Oct 2026, 12:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
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 5.7.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm fast-xml-parser: affected < 5.7.0; fixed in 5.7.0

## 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-gh4j-gqv2-49f6 (OSV record GHSA-gh4j-gqv2-49f6 lists affected ranges: npm fast-xml-parser >=0 <5.7.0 (fixed))
- Verified: https://github.com/advisories/GHSA-gh4j-gqv2-49f6 (GitHub-reviewed advisory GHSA-gh4j-gqv2-49f6 lists affected ranges: npm fast-xml-parser >=0 <5.7.0)

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