CVE-2026-81528: NoSQL injection via array replacement bypassing update shape validation in driver write path

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-27 · updated 2026-09-29
Weakness: CWE-943

Description

A MongoDB C# driver document-replacement code path omits the element-name/shape validation that the equivalent write paths apply, so a value supplied as a replacement is forwarded to the server without neutralization of query-language special elements. An application that passes untrusted, loosely-typed input as a replacement value therefore allows that input to be interpreted by the database as update logic rather than as data, executing under the application's own database credentials. Applications using strongly-typed document mappings are not affected.

Affected products

MongoDB Inc MongoDB .NET/C# Driver: from 2.10.0 before 3.11.1 — fixed in 3.11.1

How to fix

Upgrade to a fixed version: MongoDB Inc MongoDB .NET/C# Driver 3.11.1. Check the vendor advisory for mitigations.

References

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