# CVE-2026-63462: Unleash server unauthenticated denial of service via deeply nested JSON

Source: https://junglewise.ai/threats/cve-2026-63462-unleash-server-unauthenticated-denial-of-service-via-deeply  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-21. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-63462 · Severity: high · CVSS 7.5 · Published 2026-08-21

Unleash is a feature-flag management server used to control application behavior in production. An unauthenticated attacker can crash the entire server with a single 10 KB POST request containing deeply-nested JSON sent to any validation endpoint. The server does not recover automatically, and repeated requests can sustain an indefinite outage without a restart policy.

Technologies: [unleash-server (npm)](https://junglewise.ai/threats/technologies/unleash-server). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-63462 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-63462 being exploited in the wild.

**How severe is CVE-2026-63462?** High severity, with a CVSS score of 7.5, published 21 August 2026.

**Which products and versions are affected?** unleash-server (npm) SEMVER:introduced=0,fixed=7.5.2.

**Is there a fix for CVE-2026-63462?** Yes. unleash-server (npm): upgrade to 7.5.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-63462 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-63462?** Check whether you run unleash-server (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- unleash-server (npm): upgrade to 7.5.2 or later

  ```sh
  npm install unleash-server@7.5.2
  ```


## Technical details

The vulnerability is an uncontrolled recursion flaw (CWE-674) in the OpenAPI request validation error path. When validation fails, the error formatter in src/lib/error/bad-data-error.ts calls JSON.stringify(propertyValue) directly on request-body data extracted via lodash.get, with no recursion limit or try/catch wrapper. A JSON object or array nested 4000–5000 levels deep causes JSON.stringify to exceed V8's call stack, throwing RangeError: Maximum call stack size exceeded synchronously. The synchronous throw propagates through the Express error middleware openAPIValidationMiddleware in src/lib/routes/controller.ts, which has no error handler. The Node.js process registers only unhandledRejection, not uncaughtException, so the synchronous error terminates the process with exit(1). The vulnerability is route-independent, affecting all OpenAPI-validated endpoints including the anonymous POST /edge/validate and POST /edge/issue-token. Patched versions are 7.5.2, 7.6.5, and 8.0.2.

## Affected products

- Unleash unleash-server < 7.5.2, >= 7.6.0 and < 7.6.5, >= 8.0.0 and < 8.0.2

## Identifiers

- CVE-2026-63462
- GHSA-r5pq-6chh-j3xp

## Timeline

- 2026-08-21: disclosed: Advisory published on GitHub Advisory Database
- 2026-07-01: patched: Patches released as v7.5.2, v7.6.5, and v8.0.2

## References

- [https://api.github.com/users/kah-ja](https://api.github.com/users/kah-ja)
- [https://github.com/kah-ja](https://github.com/kah-ja)
- [https://api.github.com/users/kah-ja/gists%7B/gist_id%7D](https://api.github.com/users/kah-ja/gists%7B/gist_id%7D)
- [https://api.github.com/users/kah-ja/repos](https://api.github.com/users/kah-ja/repos)
- [https://avatars.githubusercontent.com/u/36455663?v=4](https://avatars.githubusercontent.com/u/36455663?v=4)
- [https://api.github.com/users/kah-ja/events%7B/privacy%7D](https://api.github.com/users/kah-ja/events%7B/privacy%7D)

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