# CVE-2026-126066: fast-xml-parser: Quadratic CPU consumption scanning unterminated stop-node tags


- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 10 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** GHSA-474x-hrwr-fgx4

## What is CVE-2026-126066?

CVE-2026-126066 is a low-severity vulnerability in NaturalIntelligence fast-xml-parser, published on 10 Nov 2026. 

### Official description

fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Prior to 5.12.0, when the non-default stopNodes option is enabled, readStopNodeData() in OrderedObjParser.js calls readTagExp() for each less-than character in an unterminated stop-node body and repeatedly rescans the remaining input while looking for a closing greater-than character. An attacker who supplies XML containing many tag fragments without a later closing character can cause quadratic rescanning before parsing fails, blocking a Node.js event loop and causing CPU-exhaustion denial of service. This issue is fixed in version 5.12.0.

Weakness: CWE-407 (Inefficient Algorithmic Complexity)

## Which versions are affected by CVE-2026-126066?

1 open source package ship an affected version, including fast-xml-parser.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `fast-xml-parser` | npm | All versions | 5.12.0 |

## How do I fix CVE-2026-126066?

Upgrade fast-xml-parser to 5.12.0 or later.

## Is CVE-2026-126066 being exploited?

There is no known exploitation of CVE-2026-126066 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126066 and fix it if it is affected.

What it is: CVE-2026-126066 is a low-severity vulnerability in NaturalIntelligence fast-xml-parser, published on 10 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-126066 in the wild and no public exploit code.

Affected packages and fixed versions:
- fast-xml-parser (npm): affected all versions; fixed in 5.12.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-126066/ (Markdown: https://insights.sbomify.com/CVE-2026-126066/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126066
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126066
- OSV: https://osv.dev/vulnerability/CVE-2026-126066

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126066/
Summaries are generated and may contain mistakes; the official description above is the record.