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CVE-2026-81528 MongoDB CVE debrief

CVE-2026-81528 is a medium-severity vulnerability in the MongoDB C# driver that allows untrusted input to be interpreted as update logic. This occurs because the driver omits element-name/shape validation in a document-replacement code path, which is applied in certain write operations. As a result, an application that passes untrusted, loosely-typed input as a replacement value may inadvertently allow that input to be executed by the database under the application's own credentials. The vulnerability primarily affects applications using loosely-typed document mappings, while applications with strongly-typed mappings are not impacted. Defenders and developers using the MongoDB C# 3

Vendor
MongoDB
Product
C# Driver
CVSS
MEDIUM 5.3
CISA KEV
Not listed in stored evidence
Original CVE published
2026-08-27
Original CVE updated
2026-09-29
Advisory published
2026-08-27
Advisory updated
2026-09-29

Who should care

Defenders and developers using MongoDB C# driver, especially those with applications using loosely-typed document mappings, should assess exposure and prioritize verification and updates.

Why it matters

CVE-2026-81528 is a medium-severity vulnerability in MongoDB C# driver that allows untrusted input to be interpreted as update logic, potentially leading to security issues. Defenders and developers should prioritize verification and updates, especially for applications using loosely-typed document mappings.

  • Verify and update MongoDB C# driver versions to prevent potential security issues
  • Review and adjust application document mappings to ensure strong typing
  • Monitor for potential security incidents related to this vulnerability

Technical summary

A vulnerability in the MongoDB C# driver allows untrusted input to be interpreted as update logic, potentially leading to security issues. The vulnerability affects applications using loosely-typed document mappings, as these do not apply the necessary validation to prevent malicious input from being executed as database commands. This can result in unauthorized data modifications or other security breaches if an attacker can supply crafted input. The vulnerability has a CVSS score of 5.3 and is classified as medium-severity. Developers should prioritize updating to a secure version of the driver and reviewing document mappings to ensure strong typing.

Defensive priority

Defenders should prioritize verifying and updating MongoDB C# driver versions, especially for applications using loosely-typed document mappings.

Recommended defensive actions

  • Verify and update MongoDB C# driver versions to 3.11.1 or later
  • Review applications using loosely-typed document mappings for potential vulnerabilities
  • Implement strongly-typed document mappings where possible
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD details indicate a medium-severity vulnerability in MongoDB C# driver, allowing untrusted input to be interpreted as update logic. Evidence is based on official CVE Program and NVD records.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-81528 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-81528

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-81528 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-81528

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.