# CVE-2026-126982: MongoDB C# Driver BSON type allow-list bypass

Source: https://junglewise.ai/threats/cve-2026-126982-a-type-allow-list-bypass-in-the-bson-serialization-library-of  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-13. Updated: 2026-11-13  
License: CC BY 4.0 with a link back

CVE-2026-126982 · Severity: high · CVSS 7.5 · Published 2026-11-13

The MongoDB C# Driver's BSON serialization library can be tricked into instantiating .NET types outside of an intended allow-list when deserializing polymorphic data. An attacker who can supply BSON or JSON data consumed by an application can instantiate arbitrary types and populate them with attacker-controlled values, potentially leading to code execution if suitable gadget types exist in the environment.

Technologies: [MongoDB C Driver](https://junglewise.ai/threats/technologies/c-driver). Vendors: [MongoDB](https://junglewise.ai/threats/vendors/mongodb).

## Quick answers

**Is CVE-2026-126982 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-126982 being exploited in the wild.

**How severe is CVE-2026-126982?** High severity, with a CVSS score of 7.5, published 13 November 2026.

**Which products and versions are affected?** MongoDB C Driver unknown.

**Is there a fix for CVE-2026-126982?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-126982 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-126982?** Check whether you run MongoDB C Driver 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.

## Technical details

The vulnerability is a type allow-list bypass in BSON deserialization that occurs when polymorphic data is deserialized into loosely typed members. An attacker can supply malicious BSON/JSON input to circumvent the type-restriction check, causing instantiation of unintended .NET types with attacker-supplied values. No special privileges are required beyond the ability to introduce data the application deserializes; exploitation may enable arbitrary code execution depending on available gadget types.

## Affected products

- MongoDB C# Driver unknown

## Timeline

- 2026-11-13: disclosed

## References

- [https://jira.mongodb.org/browse/CSHARP-6160](https://jira.mongodb.org/browse/CSHARP-6160)

## Related threats

- [MongoDB C Driver namespace field validation bypass](https://junglewise.ai/threats/cve-2026-120956-the-mongodb-c-driver-does-not-validate-the-type-or-format-of-a)
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- [MongoDB C Driver memory-initialization flaw in GridFS](https://junglewise.ai/threats/cve-2026-120684-a-memory-initialization-flaw-in-the-legacy-gridfs-file-handling)
- [MongoDB C Driver memory leak in compressed responses](https://junglewise.ai/threats/cve-2026-120678-a-memory-management-flaw-in-the-mongodb-c-driver-s-handling-of)
- [MongoDB C# Driver BSON numeric type conversion in binary subtype](https://junglewise.ai/threats/cve-2026-114654-a-numeric-type-conversion-flaw-in-the-bson-handling-library-of)